If you look in the Metalink link you will see they suggest putting
EVENT="942 TRACE NAME ERRORSTACK LEVEL 3"
in the init.ora for a specific error (ORA-00942 in this example). (Steve was trying hard to remember this).
Can this be implemented by an ALTER SYSTEM? I haven't had a chance to test.

If I did the alter system that you, vipanshrm, suggest: I'd have 100's of Mb of trace to wade through - I only see the error about once per week. And because I don't know where it is coming from, I can't provoke it! . . . Steve's suggestion only generates trace output for the error and so can be left in place for a long period - spot on.