[Zope-CMF] UnpickleableError

[seb bacon]

I'm having a really confusing time here, so my explanation / plea for
help might not make much sense.  It's further complicated by the fact
I've hacked the source in a few places and didn't version control it
(I thought it would be a 10 minute job...:)  If anyone more
experienced than I can give me their gut feeling about this, though,
I'd appreciate it.

I've fixed a problem stopping you from creating new objects in a
member's home folder over WebDAV.  All content types are created
correctly, except File types (which are the default type). 

The only client-side symptom for the failure with these types is a 500
Internal Server Error message.  If I go through the debugger, I find
an UnpickleableError is raised at the point where the transaction is
committed.  The exc_value is an UnpickleableError instance,
unhelpfully enough, so I don't know much about it.

I *can* create File types TTW.  I can also confirm that the NullResource
is correctly using a CMFDefault File factory.  The data is being stored in
the object correctly; it's just the commit which fails.

The File code is vanilla CMF CVS.  I don't have the problem with Images, which use
almost indentical code, including the same PUT (from OFS.Image).

What kind of thing causes UnpickleableErrors?  Why would Files fail
and Images work?  Why would Files fail through WebDAV and succeed TTW?
I know these are very vague questions but any pointers at all would be
useful at this point....

cheers

seb