HOW TO FIX TF400898 in your TFS Server Replacing one single DLL in TFS server could solve your problem with backlog or WORK items !!!How to solve ? You need to replace one single DLL microsoft.teamfoundation.workitemtracking.common.dll with older version.Steps: In Windows Explorer on TFS server go to C:\Windows\Microsoft.NET\assembly\GAC_MSIL\Microsoft.TeamFoundation.WorkItemTracking.Common\v4.0_12.0.0.0__b03f5f7f11d50a3a then Rename microsoft.teamfoundation.workitemtracking.common.dllfile  with something else (please don't delete DLL in case you need to undo this) Paste this file http://www.copydll.org/microsoft.teamfoundation.workitemtracking.common.dll/en-download-5536.htmlin this directory. Restarting TFS server itself of IIS services was enough for me to get r...