OK, let me clear this up, because both responses seem to have missed
what I was trying to say.

There is no problem with Firebird per se. I am not concerned about the
error, it is an invalid typecast style message, I am probably trying
to insert a string into an integer field.

When I delete the parent record, there are about 30 triggers that fire
off. One of those triggers causes this problem. At this stage it looks
like I need to remove them one at a time to trace where the error
comes from. I just thought there might be a more efficient process of
identifying the rogue trigger.