You upgraded DPM after the upgrade you can click to run any reports in "Reporting" within the DPM console and you get an error like the following:

Cannot open database "DPMDB" requested by the login. The login failed. Login failed for user ‘%servername%\DPMR$%servername%.

The account ‘%servername%\DPMR$%servername%. doesn’t have the correct mappings for the DPM database, therefore the reporting services cannot access the database to pull out the information to make the reports.

Open your DPM 2012 instance using SQL management studio.

Then expand  the Security node, then Logins; right-click %servername%\DPMDBReaders$%servername% and select properties.

Select User Mapping on the left hand side; in the upper right pane, under "Users mapped to this login:" verify DPMDB is selected; In lower right pane, ensure db_datareader and public are both selected; click OK.

Now try the report again, it should work.