This is happening to us also. The workaround is to add enough empty sections (tabs) so that the "missing" section is also found. But this is a bit ugly as the user is thrown on an empty tab + a bunch of empty tabs is floating around.
A question: where is the "current" tab stored? Is it stored for each user? How can I "reset" this to zero?
In our case the error happens if the course is entered without any login, not a guest account but as a non-logged-in user.
