Getting this error (and your TFS is installed on a Domain Controller)?
An error has occurred during report processing. (rsProcessingAborted)
Cannot impersonate user for data source ‘TfsReportDS’. (rsErrorImpersonatingUser)
Logon failed. (rsLogonFailed)
Logon failure: the user has not been granted the requested logon type at this computer. (Exception from HRESULT: 0x80070569)
Make sure that the local policy of the DC allows for login of non-admin users.
(Domain Controller Security Policy > Local Policies | User Rights Assignment | "Allow log on locally" policy and add domain users.
(Thanks to Carl Daniel who wrote about the solution in the MSDN Forums.)