[Zope] __basicnew__ errors

[seb bacon]

Whenever I try to import an object from one Zope (2.3.0) to another
(2.3.1) I get a 

  Error Type: AttributeError
  Error Value: __basicnew__

and the top of the stack is one of those indecipherable pickled
things, which I have no idea how to read or how they might be useful,
i.e.

    --   File /usr/local/Zope/lib/python/ZODB/Connection.py, line 166,
    in __getitem__ 
    (Info: ('\000\000\000\000\000\0001\030', '((U\036Pro <lots of junk
    snipped> 0tr\211\001\000\000Qu.')) 
    AttributeError: (see above)

I also get this error when I try to fire up the 2.3.1 with a copy of
the Data.fs from 2.3.0.

Why might this be?  Can anyone shed any light onto what __basicnew__
does?  And has anyone any pointers to understanding these pickled
traceback things?  Whenever they occur, I find it's usually due to
inconsistencies between the pickled product-related info and the
products loaded from the filesystem, but I don't know how to go about
debugging it.

Cheers,

seb