Dieter Mauer responded:

Dennis Allison writes:

...

I modified ZDiscussions significantly and it works fine. It's a ZClass with Python base classes. I want to export it to another Zope instance. So I simply exported it from the Control_Panel/Products menu in the ZMI. Export worked fine but when I import it in the new system, I get a diagnostic

Failed to import class _ZClass_for_ZDTopic from module Products.ZDBase

Products.ZDBase defines the ZDisscussions base classes. It was installed successfully in a separate, independent import. Did you restart Zope after you have installed the ZDBase product (and before you imported the zexp)?

yes, I did. In setting up the new site I wrote a configuration program that moves in and installs all the various products repeatably so I have a stable base. The ZClass portion ot the ZDiscussions (the zexp file) even gets copied into import for ease of installation. Just to be sure, I repeated the export process and everything worked. Such Heissenbugs bother me. I'm guessing that I may have mistyped one of the names or something. Anyhow, for the moment all is well. Thanks/