[Zope] manage_upload not found?

I can call manage_addFile to add a new file to the ZODB. If I try and add a file with the same id as an existing object, I get an error from manage_addFile. Fair enough. I looked at the source of the management interface and say manage_upload used to change the contents of an existing object. However, when I try and use this Zope is saying it cannot find it. Any ideas? regards, http://www.pyxie.org - an Open Source XML Processing library for Python