Ok - first problems is that you're running vanilla SP2, which has a bunch of bugs in maintenance plans. From the output you've sent, you're hitting the one where it repeatedly CHECKDBs master instead of the actual user database. You need to install the hotfix described in http://support.microsoft.com/kb/934459 to fix that. Then you'll *really* be running DBCC CHECKDB against the user databases.

Once you've done that and CHECKDB runs, we'll see which database has the corruption.

The stack dump looks to be coming from the cleanup part of your maintenance task, and there was also a bug there too - so the hotfix I've pointed you at above might resolve that too (it fixes the cleanup task bug).

Thanks