[Zope] ZODB BTrees File Storage error on start up

[David Pratt]

I just began receiving this error this morning in one of my event logs 
on start up. It looks serious.

2005-08-08T08:49:26 WARNING ZODB.FileStorage Failed to load database 
index: exceptions.AttributeError: type object 'BTrees._fsBTree.fsBTree' 
has no attribute '__basicnew__'

Can someone advise a course of action and what may have happened to 
generate such an error. I use CMFBTreeFolders extensively in CMF. Many 
thanks.

Regards,
David