I am using the exact same version of Joomla and CB (1.0.13 and 1.1 respectively). Fore some weird reason, i started getting this error yesterday after 3 months working flawlessly.
I have noticed that a login attempt is written to jos_session as guest. No username is recorded. Only the timestamp, session id, guest=1 and userid=0.
I have applied most of the recipes available in quite many threads.
Unfortunately, since the site is overly customized, upgrading is not an option.
I have ran through this issue before, but not so persistently.
Any hints are much welcome.
Thanks,
Nuno.