[Zope] big problem when upgrading from2.5.1 to 2.6.1

Hi, After having upgraded from Debian's Zope 2.5.1 to 2.6.1 we encounter a very big problem with some ZClasses of us. As soon as we try to go to the control panel and see our TTW product's content, we've got a traceback like the one attached to this message. It seems that some module's docstrings appear on the stack... I've googled a bit, and found that other people encountered a similar problem when upgrading, but I didn't find any answer. Is this problem known ? Any hint ? (Except doing away completely with ZClasses, which I'm already convinced of) Do you think I can downgrade to 2.5.1 without loosing anything ? (I haven't touched anything yet, doing a backup excepted) Thanks in advance. Jerome Alet