Using IBO4.2

How can I catch errors like "Required field missing"? I would like to show user my own message.
I tried to use various OnError events of TIB_Query - OnError, OnEditError,OnPostError,... - but I got always the system error (in english) and my events were not reached at all.

Any hints welcome

Riho-Rene Ellermaa
senior programmer
Hansabank