TFS 2010 Work Item Type Definition Error TF26212 when saving a work item

I have created a Work Item Definition for TFS 2010 called "KB Item" and imported it to TFS server. After some KB Items were created in TFS, I needed to update the work item definition. I made some changes and imported new KB Item definition to TFS. Now I can reate new KB Items but can't update and save KB Items created prior to definition change.

I get the following error:

TF26212: Team Foundation Server could not save your changes. There may be problems with the work item type definition. Try again or contact your Team Foundation Server administrator.

I did google it but nothing worked.

Glad it's working.

If you haven't already done so, you should add the ALLOWEXISTINGVALUE rule to the field that references the global list. That way if the global list drops a value that existing work items use then those work items will still be editable.

Just for information if others are searching for this: In my case, the problem was a field set to REQUIRED WHEN (otherField="x") and the otherField was automatically set to "x" on a state transition.

The required field is not marked as required in the work item editor, but when trying to save, the above error occurs. Solution in this case is oviously entering some text into the field.

One other item: TFS cache needs to be cleared, if working on more than one TFS server going back and forth will cause cache issues. PowerShell to clear cache. remove-item "C:\Users\$env:username\AppData\Local\Microsoft\Team Foundation\4.0\Cache*" -Force -Confirm:$false -WarningAction:SilentlyContinue -Recurse