Hi, I have migrated from 2.1.6 to 2.2.0 by copying Data.fs. Everything works except when I try to create a new ZClass, I get "Could not load oid" error. Any help how to fix it is appreciated. Thanks, Padhu Traceback (innermost last): File E:\2gtzope\lib\python\ZPublisher\Publish.py, line 222, in publish_module File E:\2gtzope\lib\python\ZPublisher\Publish.py, line 187, in publish File E:\2gtzope\lib\python\Zope\__init__.py, line 221, in zpublisher_exception_hook (Object: ElementWithAttributes) File E:\2gtzope\lib\python\ZPublisher\Publish.py, line 171, in publish File E:\2gtzope\lib\python\ZPublisher\mapply.py, line 160, in mapply (Object: manage_addZClass) File E:\2gtzope\lib\python\ZPublisher\Publish.py, line 112, in call_object (Object: manage_addZClass) File E:\2gtzope\lib\python\ZClasses\ZClass.py, line 154, in manage_addZClass (Object: ElementWithAttributes) File E:\2gtzope\lib\python\OFS\ObjectManager.py, line 260, in _setObject (Object: ElementWithAttributes) File E:\2gtzope\lib\python\ZClasses\ZClass.py, line 421, in manage_afterAdd (Object: CDClass) File E:\2gtzope\lib\python\ZClasses\ZClass.py, line 374, in _register (Object: CDClass) File E:\2gtzope\lib\python\ZODB\Connection.py, line 447, in setstate File E:\2gtzope\lib\python\ZODB\Connection.py, line 213, in _persistent_load (Info: m) File E:\2gtzope\lib\python\ZODB\Connection.py, line 154, in __getitem__ (Info: ('\000\000\000\000\000\000\005m', <------------------snip---------------> Could not load oid m, pickled data in traceback info may contain clues: (see above)