ORA-100501: non-ORACLE exception

ORA-100501 is the error returned when you trap a Raise Form_Trigger_Failure in an exception handler.

Somewhere in your program unit, you have coded

Exception... when others then...

Coding "Exception when others" is a bad idea. I have NEVER coded that phrase in a form. Take it out EVERY PLACE in your form, and your problem will disappear. The standard error processing that occurs in Forms is all you need.