[Zope] Weird intermittent error with BTreeFolder

[Chris Withers]

Hi,

Every so often, if I go to a URL like:

http://x.com/btreefolder/fileobject

I get this weird error:

Error Type: NotFound
Error Value: The object at http://x.com/btreefolder has an empty or missing 
docstring. Objects must have a docstring to be published.

Traceback (innermost last):
   File /usr/local/zope/2.5.1_base/lib/python/ZPublisher/Publish.py, line 89, in 
publish
   File /usr/local/zope/2.5.1_base/lib/python/ZPublisher/BaseRequest.py, line 
320, in traverse
   File /usr/local/zope/2.5.1_base/lib/python/ZPublisher/HTTPResponse.py, line 
502, in debugError

...where btreefolder is a version 0.2 BtreeFolder and fileobject is a normal 
Zope 2.5.1 File object.

The amazingly frustrating thing is that if I refresh the URL, things work 
exactly as I expect :-(

Any ideas?!

cheers,

Chris