Are those error messages from an application or straight from the database? If database THEN
null; -- there is no fix. Get used to it.
ELSIF application THEN
see developer; -- tell him/her to be more descriptive.
Honestly, I think 9i took a step backwards in some respects. They implemented the SQL99 standard and good DBA features, but performance went down, bugs went up, and there's issues like the one you pointed out. Unfortunately, I don't think you can do anything about the error reporting problem except apply the lateste patchset (92050) and any other relevant patches, but unfortunately I don't know of any patches specific to the error reporting subsystem. Hopefully, another dbForums user will know more.