diff --git a/src/Umbraco.Core/Persistence/Repositories/ContentTypeBaseRepository.cs b/src/Umbraco.Core/Persistence/Repositories/ContentTypeBaseRepository.cs
index 21fb9842d9..b88b928e9c 100644
--- a/src/Umbraco.Core/Persistence/Repositories/ContentTypeBaseRepository.cs
+++ b/src/Umbraco.Core/Persistence/Repositories/ContentTypeBaseRepository.cs
@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Data;
 using System.Globalization;
 using System.Linq;
 using System.Threading.Tasks;
@@ -11,6 +12,7 @@ using Umbraco.Core.Persistence.Caching;
 using Umbraco.Core.Persistence.Factories;
 using Umbraco.Core.Persistence.Querying;
 using Umbraco.Core.Persistence.Relators;
+using Umbraco.Core.Persistence.SqlSyntax;
 using Umbraco.Core.Persistence.UnitOfWork;
 
 namespace Umbraco.Core.Persistence.Repositories
@@ -63,6 +65,17 @@ namespace Umbraco.Core.Persistence.Repositories
 
         protected void PersistNewBaseContentType(ContentTypeDto dto, IContentTypeComposition entity)
         {
+            //Cannot add a duplicate content type type
+            var exists = Database.ExecuteScalar<int>(@"SELECT COUNT(*) FROM cmsContentType
+INNER JOIN umbracoNode ON cmsContentType.nodeId = umbracoNode.id
+WHERE cmsContentType." + SqlSyntaxContext.SqlSyntaxProvider.GetQuotedColumnName("alias") + @"= @alias
+AND umbracoNode.nodeObjectType = @objectType",
+                new { alias = entity.Alias, objectType = NodeObjectTypeId });
+            if (exists > 0)
+            {
+                throw new DuplicateNameException("An item with the alias " + entity.Alias + " already exists");
+            }
+
             //Logic for setting Path, Level and SortOrder
             var parent = Database.First<NodeDto>("WHERE id = @ParentId", new { ParentId = entity.ParentId });
             int level = parent.Level + 1;
@@ -165,6 +178,19 @@ namespace Umbraco.Core.Persistence.Repositories
 
         protected void PersistUpdatedBaseContentType(ContentTypeDto dto, IContentTypeComposition entity)
         {
+
+            //Cannot update to a duplicate alias
+            var exists = Database.ExecuteScalar<int>(@"SELECT COUNT(*) FROM cmsContentType
+INNER JOIN umbracoNode ON cmsContentType.nodeId = umbracoNode.id
+WHERE cmsContentType." + SqlSyntaxContext.SqlSyntaxProvider.GetQuotedColumnName("alias") + @"= @alias
+AND umbracoNode.nodeObjectType = @objectType
+AND umbracoNode.id <> @id",
+                new { id = dto.NodeId, alias = entity.Alias, objectType = NodeObjectTypeId });
+            if (exists > 0)
+            {
+                throw new DuplicateNameException("An item with the alias " + entity.Alias + " already exists");
+            }
+
             var propertyGroupFactory = new PropertyGroupFactory(entity.Id);
 
             var nodeDto = dto.NodeDto;
diff --git a/src/Umbraco.Core/Persistence/Repositories/DataTypeDefinitionRepository.cs b/src/Umbraco.Core/Persistence/Repositories/DataTypeDefinitionRepository.cs
index d8bfe62deb..3798bb53d9 100644
--- a/src/Umbraco.Core/Persistence/Repositories/DataTypeDefinitionRepository.cs
+++ b/src/Umbraco.Core/Persistence/Repositories/DataTypeDefinitionRepository.cs
@@ -165,6 +165,18 @@ WHERE umbracoNode." + SqlSyntaxContext.SqlSyntaxProvider.GetQuotedColumnName("te
 
         protected override void PersistUpdatedItem(IDataTypeDefinition entity)
         {
+
+            //Cannot change to a duplicate alias
+            var exists = Database.ExecuteScalar<int>(@"SELECT COUNT(*) FROM cmsDataType
+INNER JOIN umbracoNode ON cmsDataType.nodeId = umbracoNode.id
+WHERE umbracoNode." + SqlSyntaxContext.SqlSyntaxProvider.GetQuotedColumnName("text") + @"= @name
+AND umbracoNode.id <> @id", 
+                    new { id = entity.Id, name = entity.Name });
+            if (exists > 0)
+            {
+                throw new DuplicateNameException("A data type with the name " + entity.Name + " already exists");
+            }
+
             //Updates Modified date and Version Guid
             ((DataTypeDefinition)entity).UpdatingEntity();
 
diff --git a/src/Umbraco.Core/Persistence/Repositories/RepositoryBase.cs b/src/Umbraco.Core/Persistence/Repositories/RepositoryBase.cs
index f14a88ba74..0932cc89b2 100644
--- a/src/Umbraco.Core/Persistence/Repositories/RepositoryBase.cs
+++ b/src/Umbraco.Core/Persistence/Repositories/RepositoryBase.cs
@@ -223,8 +223,19 @@ namespace Umbraco.Core.Persistence.Repositories
         /// <param name="entity"></param>
         public virtual void PersistNewItem(IEntity entity)
         {
-            PersistNewItem((TEntity)entity);
-            _cache.Save(typeof(TEntity), entity);
+            try
+            {
+                PersistNewItem((TEntity)entity);
+                _cache.Save(typeof(TEntity), entity);
+            }
+            catch (Exception)
+            {
+                //if an exception is thrown we need to remove the entry from cache, this is ONLY a work around because of the way
+                // that we cache entities: http://issues.umbraco.org/issue/U4-4259
+                _cache.Delete(typeof (TEntity), entity);
+                throw;
+            }
+            
         }
 
         /// <summary>
@@ -233,8 +244,19 @@ namespace Umbraco.Core.Persistence.Repositories
         /// <param name="entity"></param>
         public virtual void PersistUpdatedItem(IEntity entity)
         {
-            PersistUpdatedItem((TEntity)entity);
-            _cache.Save(typeof(TEntity), entity);
+            try
+            {
+                PersistUpdatedItem((TEntity)entity);
+                _cache.Save(typeof(TEntity), entity);
+            }
+            catch (Exception)
+            {
+                //if an exception is thrown we need to remove the entry from cache, this is ONLY a work around because of the way
+                // that we cache entities: http://issues.umbraco.org/issue/U4-4259
+                _cache.Delete(typeof (TEntity), entity);
+                throw;
+            }
+            
         }
 
         /// <summary>
diff --git a/src/Umbraco.Tests/Membership/UmbracoServiceMembershipProviderTests.cs b/src/Umbraco.Tests/Membership/UmbracoServiceMembershipProviderTests.cs
index 64305d6b1c..99ec6dbef2 100644
--- a/src/Umbraco.Tests/Membership/UmbracoServiceMembershipProviderTests.cs
+++ b/src/Umbraco.Tests/Membership/UmbracoServiceMembershipProviderTests.cs
@@ -95,7 +95,7 @@ namespace Umbraco.Tests.Membership
             mServiceMock.Setup(service => service.GetDefaultMemberType()).Returns("Member");
             mServiceMock.Setup(
                 service => service.CreateWithIdentity(It.IsAny<string>(), It.IsAny<string>(), It.IsAny<string>(), It.IsAny<string>()))
-                        .Callback((string u, string e, string p, string m, bool b) =>
+                        .Callback((string u, string e, string p, string m) =>
                             {
                                 createdMember = new Member("test", e, u, p, memberType);
                             })
@@ -126,7 +126,7 @@ namespace Umbraco.Tests.Membership
             mServiceMock.Setup(service => service.GetDefaultMemberType()).Returns("Member");
             mServiceMock.Setup(
                 service => service.CreateWithIdentity(It.IsAny<string>(), It.IsAny<string>(), It.IsAny<string>(), It.IsAny<string>()))
-                        .Callback((string u, string e, string p, string m, bool b) =>
+                        .Callback((string u, string e, string p, string m) =>
                             {
                                 createdMember = new Member("test", e, u, p, memberType);
                             })
@@ -159,7 +159,7 @@ namespace Umbraco.Tests.Membership
             mServiceMock.Setup(service => service.GetDefaultMemberType()).Returns("Member");
             mServiceMock.Setup(
                 service => service.CreateWithIdentity(It.IsAny<string>(), It.IsAny<string>(), It.IsAny<string>(), It.IsAny<string>()))
-                        .Callback((string u, string e, string p, string m, bool b) =>
+                        .Callback((string u, string e, string p, string m) =>
                         {
                             createdMember = new Member("test", e, u, p, memberType);
                         })
diff --git a/src/Umbraco.Web.UI/umbraco/controls/ContentTypeControlNew.ascx b/src/Umbraco.Web.UI/umbraco/controls/ContentTypeControlNew.ascx
index 16f5ba6d53..3a9bd18b96 100644
--- a/src/Umbraco.Web.UI/umbraco/controls/ContentTypeControlNew.ascx
+++ b/src/Umbraco.Web.UI/umbraco/controls/ContentTypeControlNew.ascx
@@ -52,7 +52,8 @@
     
     <cc2:PropertyPanel ID="pp_alias" runat="server" Text="Alias">
          <asp:TextBox ID="txtAlias" CssClass="guiInputText guiInputStandardSize" runat="server"></asp:TextBox>
-         <asp:RequiredFieldValidator ControlToValidate="txtAlias" runat="server" ErrorMessage="Alias cannot be empty!"></asp:RequiredFieldValidator>
+         <asp:RequiredFieldValidator Display="Dynamic" ControlToValidate="txtAlias" runat="server" ErrorMessage="Alias cannot be empty!"></asp:RequiredFieldValidator>
+        <asp:CustomValidator Display="Dynamic" runat="server" ID="DuplicateAliasValidator" ErrorMessage="A type with this alias already exists"></asp:CustomValidator>
     </cc2:PropertyPanel>
   </cc2:Pane>
   
diff --git a/src/Umbraco.Web.UI/umbraco/controls/ContentTypeControlNew.ascx.cs b/src/Umbraco.Web.UI/umbraco/controls/ContentTypeControlNew.ascx.cs
index c3459b752e..28250d9fa4 100644
--- a/src/Umbraco.Web.UI/umbraco/controls/ContentTypeControlNew.ascx.cs
+++ b/src/Umbraco.Web.UI/umbraco/controls/ContentTypeControlNew.ascx.cs
@@ -2,6 +2,7 @@
 using System.Collections.Generic;
 using System.Linq;
 using System.Web;
+using System.Web.UI.WebControls;
 
 namespace Umbraco.Web.UI.Umbraco.Controls
 {
diff --git a/src/Umbraco.Web.UI/umbraco/controls/ContentTypeControlNew.ascx.designer.cs b/src/Umbraco.Web.UI/umbraco/controls/ContentTypeControlNew.ascx.designer.cs
index 582c67837d..c17c27becf 100644
--- a/src/Umbraco.Web.UI/umbraco/controls/ContentTypeControlNew.ascx.designer.cs
+++ b/src/Umbraco.Web.UI/umbraco/controls/ContentTypeControlNew.ascx.designer.cs
@@ -11,5 +11,7 @@ namespace Umbraco.Web.UI.Umbraco.Controls {
     
     
     public partial class ContentTypeControlNew {
+        
+        
     }
 }
diff --git a/src/Umbraco.Web.UI/umbraco/create/simple.ascx b/src/Umbraco.Web.UI/umbraco/create/simple.ascx
index 4a965a4eb1..a057cb3d98 100644
--- a/src/Umbraco.Web.UI/umbraco/create/simple.ascx
+++ b/src/Umbraco.Web.UI/umbraco/create/simple.ascx
@@ -17,6 +17,6 @@
 
 <!-- added to support missing postback on enter in IE -->
 <asp:TextBox runat="server" style="visibility:hidden;display:none;" ID="Textbox1"/>
-<asp:CustomValidator runat="server" ID="CustomValidation" style="color:#8a1f11;display:block;"></asp:CustomValidator>
+<asp:CustomValidator runat="server" ID="CustomValidation" ForeColor="red" style="display:block;"></asp:CustomValidator>
 <input type="hidden" name="nodeType">
 
diff --git a/src/Umbraco.Web/Umbraco.Web.csproj b/src/Umbraco.Web/Umbraco.Web.csproj
index 49169694a6..4323ad38f8 100644
--- a/src/Umbraco.Web/Umbraco.Web.csproj
+++ b/src/Umbraco.Web/Umbraco.Web.csproj
@@ -686,6 +686,9 @@
     <Compile Include="umbraco.presentation\umbraco\create\simple.ascx.cs">
       <SubType>ASPXCodeBehind</SubType>
     </Compile>
+    <Compile Include="umbraco.presentation\umbraco\developer\DataTypes\editDatatype.aspx.cs">
+      <SubType>ASPXCodeBehind</SubType>
+    </Compile>
     <Compile Include="umbraco.presentation\umbraco\developer\Packages\directoryBrowser.aspx.cs">
       <SubType>ASPXCodeBehind</SubType>
     </Compile>
diff --git a/src/Umbraco.Web/umbraco.presentation/umbraco/controls/ContentTypeControlNew.ascx.cs b/src/Umbraco.Web/umbraco.presentation/umbraco/controls/ContentTypeControlNew.ascx.cs
index c9d049c10f..e5a883955f 100644
--- a/src/Umbraco.Web/umbraco.presentation/umbraco/controls/ContentTypeControlNew.ascx.cs
+++ b/src/Umbraco.Web/umbraco.presentation/umbraco/controls/ContentTypeControlNew.ascx.cs
@@ -334,7 +334,17 @@ namespace umbraco.controls
                         SavingContentType(_contentType);
                     }
 
-                    _contentType.Save();
+                    try
+                    {
+                        _contentType.Save();
+                    }
+                    catch (DuplicateNameException ex)
+                    {
+                        DuplicateAliasValidator.IsValid = false;
+                        asyncState.SaveArgs.IconType = BasePage.speechBubbleIcon.error;
+                        asyncState.SaveArgs.Message = ex.Message;
+                        return;
+                    }
 
                     Trace.Write("ContentTypeControlNew", "task completing");
                 };
@@ -1602,5 +1612,14 @@ jQuery(document).ready(function() {{ refreshDropDowns(); }});
         /// To modify move field declaration from designer file to code-behind file.
         /// </remarks>
         protected global::System.Web.UI.WebControls.Literal checkTxtAliasJs;
+
+        /// <summary>
+        /// DuplicateAliasValidator control.
+        /// </summary>
+        /// <remarks>
+        /// Auto-generated field.
+        /// To modify move field declaration from designer file to code-behind file.
+        /// </remarks>
+        protected global::System.Web.UI.WebControls.CustomValidator DuplicateAliasValidator;
     }
 }
\ No newline at end of file
diff --git a/src/Umbraco.Web/umbraco.presentation/umbraco/create/nodeType.ascx.cs b/src/Umbraco.Web/umbraco.presentation/umbraco/create/nodeType.ascx.cs
index ba73303dfb..3cb32f364b 100644
--- a/src/Umbraco.Web/umbraco.presentation/umbraco/create/nodeType.ascx.cs
+++ b/src/Umbraco.Web/umbraco.presentation/umbraco/create/nodeType.ascx.cs
@@ -1,5 +1,7 @@
+using System.Globalization;
 using Umbraco.Core;
 using Umbraco.Web.UI;
+using Umbraco.Web;
 
 namespace umbraco.cms.presentation.create.controls
 {
@@ -20,21 +22,21 @@ namespace umbraco.cms.presentation.create.controls
 	{
 
 
-		protected void Page_Load(object sender, System.EventArgs e)
+		protected void Page_Load(object sender, EventArgs e)
 		{
 			sbmt.Text = ui.Text("create");
             pp_name.Text = ui.Text("name");
 
             if (!IsPostBack)
             {
-                string nodeId = umbraco.helper.Request("nodeId");
+                string nodeId = Request.GetItemAsString("nodeId");
                 if (String.IsNullOrEmpty(nodeId) || nodeId == "init")
                 {
                     masterType.Items.Add(new ListItem(ui.Text("none") + "...", "0"));
-                    foreach (cms.businesslogic.web.DocumentType dt in cms.businesslogic.web.DocumentType.GetAllAsList())
+                    foreach (DocumentType dt in DocumentType.GetAllAsList())
                     {
                         //                    if (dt.MasterContentType == 0)
-                        masterType.Items.Add(new ListItem(dt.Text, dt.Id.ToString()));
+                        masterType.Items.Add(new ListItem(dt.Text, dt.Id.ToString(CultureInfo.InvariantCulture)));
                     }
                 }
                 else
@@ -58,7 +60,7 @@ namespace umbraco.cms.presentation.create.controls
                 e.IsValid = false;
         }
 
-		protected void sbmt_Click(object sender, System.EventArgs e)
+		protected void sbmt_Click(object sender, EventArgs e)
 		{
 			if (Page.IsValid) 
 			{
@@ -67,12 +69,12 @@ namespace umbraco.cms.presentation.create.controls
 					createTemplateVal = 1;
 
                 // check master type
-                var masterTypeVal = String.IsNullOrEmpty(umbraco.helper.Request("nodeId")) || umbraco.helper.Request("nodeId") == "init" ? masterType.SelectedValue : umbraco.helper.Request("nodeId");
+                string masterTypeVal = String.IsNullOrEmpty(Request.GetItemAsString("nodeId")) || Request.GetItemAsString("nodeId") == "init" ? masterType.SelectedValue : Request.GetItemAsString("nodeId");
 
                 var returnUrl = LegacyDialogHandler.Create(
                     new HttpContextWrapper(Context),
                     BasePage.Current.getUser(),
-                    helper.Request("nodeType"),
+                    Request.GetItemAsString("nodeType"),
                     createTemplateVal,
 					rename.Text,
                     int.Parse(masterTypeVal));
@@ -85,24 +87,5 @@ namespace umbraco.cms.presentation.create.controls
 			}
 		
 		}
-		#region Web Form Designer generated code
-		override protected void OnInit(EventArgs e)
-		{
-			//
-			// CODEGEN: This call is required by the ASP.NET Web Form Designer.
-			//
-			InitializeComponent();
-			base.OnInit(e);
-		}
-		
-		/// <summary>
-		///		Required method for Designer support - do not modify
-		///		the contents of this method with the code editor.
-		/// </summary>
-		private void InitializeComponent()
-		{
-
-		}
-		#endregion
 	}
 }
diff --git a/src/Umbraco.Web/umbraco.presentation/umbraco/create/simple.ascx.cs b/src/Umbraco.Web/umbraco.presentation/umbraco/create/simple.ascx.cs
index f8d8bb8e1a..dd09363c34 100644
--- a/src/Umbraco.Web/umbraco.presentation/umbraco/create/simple.ascx.cs
+++ b/src/Umbraco.Web/umbraco.presentation/umbraco/create/simple.ascx.cs
@@ -52,7 +52,7 @@ namespace umbraco.cms.presentation.create.controls
                 }
                 catch (Exception ex)
                 {
-                    CustomValidation.ErrorMessage = ex.Message;
+                    CustomValidation.ErrorMessage = "* " + ex.Message;
                     CustomValidation.IsValid = false;
                 }
             }
diff --git a/src/Umbraco.Web/umbraco.presentation/umbraco/settings/EditMediaType.aspx.cs b/src/Umbraco.Web/umbraco.presentation/umbraco/settings/EditMediaType.aspx.cs
index a20106a0cb..93e060c01d 100644
--- a/src/Umbraco.Web/umbraco.presentation/umbraco/settings/EditMediaType.aspx.cs
+++ b/src/Umbraco.Web/umbraco.presentation/umbraco/settings/EditMediaType.aspx.cs
@@ -48,24 +48,5 @@ namespace umbraco.cms.presentation.settings
             return false;
         }
 
-        #region Web Form Designer generated code
-        override protected void OnInit(EventArgs e)
-        {
-            //
-            // CODEGEN: This call is required by the ASP.NET Web Form Designer.
-            //
-            InitializeComponent();
-            base.OnInit(e);
-        }
-
-        /// <summary>
-        /// Required method for Designer support - do not modify
-        /// the contents of this method with the code editor.
-        /// </summary>
-        private void InitializeComponent()
-        {
-
-        }
-        #endregion
     }
 }
diff --git a/src/umbraco.cms/businesslogic/datatype/DataTypeDefinition.cs b/src/umbraco.cms/businesslogic/datatype/DataTypeDefinition.cs
index c58f9ac17e..4e0a48ad93 100644
--- a/src/umbraco.cms/businesslogic/datatype/DataTypeDefinition.cs
+++ b/src/umbraco.cms/businesslogic/datatype/DataTypeDefinition.cs
@@ -34,6 +34,7 @@ namespace umbraco.cms.businesslogic.datatype
         private string _propertyEditorAlias;
 
         private static readonly Guid ObjectType = new Guid(Constants.ObjectTypes.DataType);
+        private string _text1;
 
         #endregion
 
@@ -54,6 +55,13 @@ namespace umbraco.cms.businesslogic.datatype
         #endregion
 
         #region Public Properties
+
+        public override string Text
+        {
+            get { return _text1 ?? (_text1 = base.Text); }
+            set { _text1 = value; }
+        }
+
         /// <summary>
         /// The associated datatype, which delivers the methods for editing data, editing prevalues see: umbraco.interfaces.IDataType
         /// </summary>
@@ -148,6 +156,23 @@ namespace umbraco.cms.businesslogic.datatype
         /// </summary>
         public override void Save()
         {
+            //Cannot change to a duplicate alias
+            var exists = Database.ExecuteScalar<int>(@"SELECT COUNT(*) FROM cmsDataType
+INNER JOIN umbracoNode ON cmsDataType.nodeId = umbracoNode.id
+WHERE umbracoNode." + SqlSyntaxContext.SqlSyntaxProvider.GetQuotedColumnName("text") + @"= @name
+AND umbracoNode.id <> @id",
+                    new { id = this.Id, name = this.Text });
+            if (exists > 0)
+            {
+                ApplicationContext.Current.ApplicationCache.RuntimeCache.ClearCacheItem(
+                    string.Format("{0}{1}", CacheKeys.DataTypeCacheKey, this.Id));
+
+                throw new DuplicateNameException("A data type with the name " + this.Text + " already exists");
+            }
+
+            //this actually does the persisting.
+            base.Text = _text1;
+
             OnSaving(EventArgs.Empty);
         }
 
diff --git a/src/umbraco.cms/businesslogic/media/MediaType.cs b/src/umbraco.cms/businesslogic/media/MediaType.cs
index c597774472..5f00c9388a 100644
--- a/src/umbraco.cms/businesslogic/media/MediaType.cs
+++ b/src/umbraco.cms/businesslogic/media/MediaType.cs
@@ -91,12 +91,12 @@ namespace umbraco.cms.businesslogic.media
         /// <param name="Text">The name of the MediaType</param>
         /// <returns>The new MediaType</returns>
         [Obsolete("Obsolete, Use Umbraco.Core.Models.MediaType and Umbraco.Core.Services.ContentTypeService.Save()", false)]
-        public static MediaType MakeNew(BusinessLogic.User u, string Text)
+        public static MediaType MakeNew(User u, string Text)
         {
             return MakeNew(u, Text, -1);
         }
 
-        internal static MediaType MakeNew(BusinessLogic.User u, string text, int parentId)
+        internal static MediaType MakeNew(User u, string text, int parentId)
         {
             var mediaType = new Umbraco.Core.Models.MediaType(parentId) { Name = text, Alias = text, CreatorId = u.Id, Thumbnail = "folder.png", Icon = "folder.gif" };
             ApplicationContext.Current.Services.ContentTypeService.Save(mediaType, u.Id);