Forms4.5 Problems Please Help Urgently

Hi Forms Gurus,

I am new to Forms 4.5 and I have these problems. Would appreciate your help.

1. If a POPUP LIST is defined in a form at the start of development and this is subsequently changed to COMBO BOX , during runtime , the record group populates nothing and generates a General Protection Failure message in all subsequent executions . Is there a way to do this without getting an error