You want to change or have already changed the DPM SQL Reporting Services account password DPMR$<DPMSERVERNAME> after initial install of DPM.
Now when you try to access DPM reports you get this error:
An error has occurred during report processing. (rsProcessingAborted)
Cannot impersonate user for data source ‘DLS’. (rsErrorImpersonatingUser)
Log on failed. Ensure the user name and password are correct. (rsLogonFailed)
Logon failure: unknown user name or bad password
You need to modify the DPMR$<DPMSERVERNAME> password in SSRS also.
To do this go to:
Click on the DPM Reports folder
Then click on the DPMReporterDataSource object
Update the password for the account under "Credentials stored securely in the report server"
Click "Test Connection" to make sure it is working. Once confirmed click "Apply".
Now Reports should work again.