[Zope] Making __getattr__ accessible

Hi, I have an External Method that returns an instance of a class that implements its own __getattr__ method, but Python scripts inside Zope can't seem to access it (I get an 'Unauthorized' exception). I've tried adding a ClassSecurityInfo instance to declare __getattr__ public, and I've also tried deriving the class from Acquisition.Implicit, but Zope still doesn't like it. Any ideas? Thanks in advance, Dave