Thank you everyone for your help.
David, right now I can't give you any code of the application, since I'm at home, and I have nothing here. Tomorrow at work I'll give you more details about the error.
Andreas, thank you for telling me about the Python logging module. I had never debugged a Zope application before, so this is all new for me. I will read the documentation on that module, and see if I can solve my problem.
I'll keep you updated on my improvements. Once again, thank you all :)