You want to change or have already changed the DPM SQL Reporting Services account password DPMR$<DPMSERVERNAME> after initial install of DPM.
Now when you try to access DPM reports you get this error:
An error has occurred during report processing. (rsProcessingAborted)
Cannot impersonate user for data source ‘DLS’. (rsErrorImpersonatingUser)
Log on failed. Ensure the user name and password are correct. (rsLogonFailed)