[Zope] Removing tracebacks from error message

I thought I solved this problem a while ago, but if so I can't remember how. I have a custom error page in Zope (2.1.6), but Zope wants to put the traceback information into an HTML comment at the foot of the page (which I don't want to have there). I set BOBO_DEBUG_MODE=0 and exported it in the "start" script, and also removed the "-D" from the command line that launches Z2.py. I thought that was all there was to it, but there must be something else that I've forgotten. Any ideas? Thanks. David Trudgett