This error occurs instead of displaying the expected list content (such as workitem, build and source control information).
- Delete the contents of the Cache folder. The cache folder's location is specified in the main SharePoint web.config file as an application setting with key WorkItemTrackingCacheRoot. If this information is missing, the default location is under \ProgramData\Microsoft\Team Foundation\Web Access.
- After deletion the next reload of the TFS Project Portal page should rebuild this cache and restore the expected display of the TWA webparts.
If there is a significant amount of cached data, which can occur if there are a large number of TFS Team Projects or users, the subsequent first page- load attempt may report a timeout error. If this occurs, the timeout and executiontimeout values in the web.config file for the root SharePoint site should be increased to allow for complete cache regeneration.
More information about Timeout settings in SharePoint is available in the following article:
925083 Error "Request timed out" when you try to upload a large file to a document library on a Windows SharePoint Services 3.0 site