Zopists: I noticed a bug report (number and name as per subject) that sounds like the same problem I have found: If the 'XMLDocument' product is in the .../Products/ directory attempts to add a ZClass to a product fail. Editing the XMLDocument/__init__.py files initialize method so that context.registerBaseClass is only called once (for XMLDocument.XMLDocument) allows ZClasses to be added to a product. I don't think this is due to particulars of the XMLDocument product, In a product I am working on the presence of more than one 'context.registerBaseClass' call in the 'initialize; method also causes problems. The behavior is the same under both zope 2.0.0b4 and b5 on redhat/mandrake 6.0 with kernel 2.2.9. Should it be possible to register more than one python base class in a single product?