I do have a script that runs every day, but I don't think that is the problem because it doesn't touch sessions. In the application itself, one of the things I store in is a list of URL objects in the session. Every time a user logs in, the menu is generated based on that user's permissions an stored in the session. This isn't usually a problem until about the time the session expires. You get the error the next time it asks you to log in. And for some reason, restarting web2py fixes the problem.
I am still trying to determine if it's something application specific, but I haven't found anything yet.
