I have been having the exact problems in my setup. Looks like you need to go into the Setup file under lib/python and edit out all BTree, etc., build lines. What will happen is that Zope will instead build the BTree stuff using the Setup in ZopeZODB3. The only difference that I can see between lib/python/Setup and lib/python/ZopeZODB3/Setup is in the include parameters. So, instead of doing: (in lib/python/Setup, note: I commented these lines out to make things work) BTree ../Components/BTree/BTree.c -I../Components/ExtensionClass -I../Components/BTree -I./BoboPOS IIBTree ../Components/BTree/IIBTree.c -I../Components/ExtensionClass -I../Components/BTree -I./BoboPOS IOBTree ../Components/BTree/IOBTree.c -I../Components/ExtensionClass -I../Components/BTree -I./BoboPOS OIBTree ../Components/BTree/OIBTree.c -I../Components/ExtensionClass -I../Components/BTree -I./BoboPOS intSet ../Components/BTree/intSet.c -I../Components/ExtensionClass -I../Components/BTree -I./BoboPOS You should instead be using: (in lib/python/ZopeZODB3/Setup) BTree ../../Components/BTree/BTree.c -I../../Components/ExtensionClass -I../../Components/BTree -I../ZODB IIBTree ../../Components/BTree/IIBTree.c -I../../Components/ExtensionClass -I../../Components/BTree -I../ZODB IOBTree ../../Components/BTree/IOBTree.c -I../../Components/ExtensionClass -I../../Components/BTree -I../ZODB OIBTree ../../Components/BTree/OIBTree.c -I../../Components/ExtensionClass -I../../Components/BTree -I../ZODB intSet ../../Components/BTree/intSet.c -I../../Components/ExtensionClass -I../../Components/BTree -I../ZODB I suppose that's as clear as mud (esp. considering how effective I have been lately with the English language trying do describe technical stuff), but hopefully it will work for you. I guess the problem is some ZODB2 vs. ZODB3 thing, but I find it kinda interesting that we only are seeing the problem trying to add ZClass. Of course I don't know much about Zope, so there's quite a bit out there that (pleasantly) surprises me. Ciao, John M. Miller