If the history on the maintenance plan shows as successful, you have a backup file for all system databases and the job has failed, most likely the reason is because the client tools used to create the plan are older than the instance.
Validate that your client tools are upgraded to at least SP3 and the server is at least post SP2 (9.0.3054 is minimum).
Jeffrey Williams
“We are all faced with a series of great opportunities brilliantly disguised as impossible situations.”
― Charles R. Swindoll
How to post questions to get better answers faster
Managing Transaction Logs