FWIW, I can also report this problem with ZDiscussions. In my case it stemmed from not properly deleting the ZDiscussion product before moving my Data.fs from 2.1.6 to 2.2.1 (I think). The symptom then was beeing unable to create ZSQL Methods (!) because of a missing ../Products/ZDBase/ZDiscussions.py file which I "fixed" by installing ZDBase again
Man that's weird. But it's good info. Does the current PTK include ZDiscussions?
I can however NOT import the ZDiscussions.zexp anymore because of "Duplicate Class Ids".
So it looks like a ZClass didn't get cleaned up properly when you deleted the ZDiscussions through-the-web product. It might mean that there's a reference to an object in that area somewhere else in the ZODB. It'd be interesting for someone (not me, I'm booked) to think about how to write a tool that could detect orphaned instances and "strange" references in the ZODB.