I found an old case here where that ORA-12505 error happened. The case number is ISS03715375. I am telling you the case number so that if you later open a new case with BMC you can mention ISS03715375 and maybe that will help.
The customer in ISS03715375 had run out of disk space for his database and also the Oracle UNDO tablespace was too small.
Dan I think the problem is in that DB is called using service name instead of SID ...
Service Name is not supported unfortunately ...