Accessing session variables fails occasionally--perhaps once every 10000 references or so! (See collector issue #848 where I just added a comment.) Presumably this is a read conflict in temporary_folder. The access to the variable uses a python script-- request=container.REQUEST try: session=request['SESSION'] return session[varname] except KeyError: container.oopsSession( varname ) raise oopsSession() is a debug routine which reports that it cannot find REQUEST. This is Zope 2.6.2b3 and Python 2.1.3. This version of Zope is patched to NOT use the (flawed) LowConflictConnection for temporary storage. This is a critical bug for us and is becoming more so as our usage grows. It's a showstopper for our users as we are entirely session based! It's fairly likely that some internal data structure gets corrupted. We tend to fetch session variables in clusters, and when one fails all subsequent ones fail. Sad to say, the failure kills the user's session and releases a burst of emotional energy )-: Any suggestions for a fix or workaround? This particular bug has been seen in 2.7.4 so upgrading is not going to fix things.