[Zope] _delObject errors

When I try to call self._delObject('foo') from my Product, it seems to work, but I get an error logged: AttributeError: 'string' object has no attribute 'manage_beforeDelete' The offending line is in ObjectManager.py: def _delObject(self, id, dp=1): object=self._getOb(id) try: object.manage_beforeDelete(object, self) So, it would appear that self.getOb('foo') returns a string rather than whatever it's expecting. I presume this is because the object I'm deleting doesn't have some requisite base class to make it zope-manageable. It's a ZClass which has ZObject as its only base class. Am I missing something? Cheers, seb