If you have re-imported the management pack recently, the role configuration may be corrupted. Open the DPM-specific roles ...

4) If you have re-imported the management pack recently, the role configuration may be corrupted. Open the DPM-specific roles and check if the roles have tasks assigned to them. If not, delete the roles and recreate them. For more information on how to recreate the roles, see http://go.microsoft.com/fwlink/p/?LinkId=234368.