FRM-40502: ORACLE error: unable to read list of values.
Cause: A fatal error occurred while trying to read a list of values.
Action: Contact your DBA or an Oracle support representative.
I was working with a form with 6i release, converted to 10g. In that while clicking F9 for LOV in one of the fields, I encountered this error. I started debugging the form, starting from Field, LOV, Record Group. There were no problems at first sight.
I copied the SQL query from the record group and ran it in SQL*Plus, there was no problems. The query was using some bind variables from inside the form. I had modified these fields with values.
I then tried to run exactly the same where clause of the query (I commented out the bind variables) and ran the form. Bingo! It worked and the FRM-4502 error suddenly is gone.
I then tried to run the previous query (with bind variables), now also the error did not came.
I suppose this error is due to the ID of the field with which Forms works rather than the name.
It made a super note for me today...
Hope if you are in same mood, use this logic to solve your problem.