Error when creating user

[Jeremy]

Hard to tell if I am posting in the right spot, so please direct me where I can get help if this is not the right area. We are getting the following error when trying to create/edit a user from the backend admin pages. The last time we had this issue, we deleted and recreated the custom fields in the default profile which resolved the problem but it did not this time. Next we just removed the custom fields altogether which still did not resolve the issue. Any direction on how to troubleshoot this error would be much appreciative. 
 
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Timestamp: 12/17/2012 3:49:30 AM

Message: HandlingInstanceID: 688162f2-ef47-472b-92d4-051111ecc449
An exception of type 'Telerik.Sitefinity.SitefinityExceptions.ItemNotFoundException' occurred and was caught.
-------------------------------------------------------------------------------------------------------------
12/16/2012 21:49:30
Type : Telerik.Sitefinity.SitefinityExceptions.ItemNotFoundException, Telerik.Sitefinity, Version=5.1.3270.0, Culture=neutral, PublicKeyToken=b28c218413bdf563
Message : You are trying to access item that no longer exists. The most probable reason is that it has been deleted by another user.
Source : Telerik.Sitefinity
Help link : 
Data : System.Collections.ListDictionaryInternal
TargetSite : TItem GetItemById[TItem](Telerik.Sitefinity.Data.OA.SitefinityOAContext, System.String)
Stack Trace :    at Telerik.Sitefinity.Data.OpenAccessExtensions.GetItemById[TItem](SitefinityOAContext oaContext, String id)
   at Telerik.Sitefinity.Taxonomies.Data.OpenAccessTaxonomyProvider.GetTaxonomy(Guid id)
   at Telerik.Sitefinity.Taxonomies.TaxonomyManager.GetTaxonomy(Guid id)
   at Telerik.Sitefinity.Web.UI.Fields.TaxonField.get_Taxonomy()
   at Telerik.Sitefinity.Web.UI.Fields.FlatTaxonField.InitializeControls(GenericContainer container)
   at Telerik.Sitefinity.Web.UI.SimpleView.CreateChildControls()
   at System.Web.UI.Control.EnsureChildControls()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Control.PreRenderRecursiveInternal()
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

Additional Info:

MachineName : 1
TimeStamp : 12/17/2012 3:49:30 AM
FullName : Telerik.Sitefinity.Utilities, Version=5.1.3270.0, Culture=neutral, PublicKeyToken=b28c218413bdf563
AppDomainName : /LM/W3SVC/2/ROOT-1-130001894513920746
ThreadIdentity : USER1
WindowsIdentity : IIS APPPOOL\APP4
Requested URL : http://localhost/Sitefinity/Dialog/UserEditDialog


Category: ErrorLog

Priority: 0

EventId: 90000

Severity: Error

Title:Enterprise Library Exception Handling

Machine: 1

App Domain: /LM/W3SVC/2/ROOT-1-130001894513920746

ProcessId: 1880

Process Name: c:\windows\system32\inetsrv\w3wp.exe

Thread Name: 

Win32 ThreadId:4656

Extended Properties: 

[Strahil Strahilov]

Hello Jeremy,
Thank you for contacting us.
The reason for your issue is that you have a custom field(s) based on a classification that no longer exists. We strongly recommend  to upgrade your project to the latest Sitefinity version. With this upgrade you won't be able to delete Classifications, that are being used.
However to manage your current situation, you will probably need to manually clean up your database.

1. First backup your database;
2. you should find a table called - sf_sitefinity_profile_<the name of  the custom field>;
3. Remove that table;
4. Go through Administration -> Users -> Manage Profile types -> <choose your profile>;
5. Remove all fields that are based on classifications;

Step 2 and 3 are not recommended, because it is good to clean your Database. However if you follow step 1, 3 and 4 it will be enough to fix your issue.

All the best,
Strahil Strahilov
the Telerik team