After moving a reporting services database from SQL server 2008r2 to 2012, we had a problem running reports in TFS.
The error was:
An error has occurred during report processing. (rsProcessingAborted)
Cannot impersonate user for data source ‘TfsReportDS’. (rsErrorImpersonatingUser)
Log on failed. Ensure the user name and password are correct. (rsLogonFailed)
For more information about this error navigate to the report server on the local server machine, or enable remote errors
Add a local policy on the SQL server allowing the Report Services User (Reader Account in TFS Admin console) to log on locally or add it to a group which already has these rights.