Firstly you'll need to go back to the computer on which you logged on to the supervisor.
Log in again with the username that you logged on. You should be able to log in again and
then log off.
Alternatively if it is a large network where it is difficult to find the computer, who's
IP address it is, log in to the Administrator and then stop and start the Supervisor service.
That will log off all currently logged in supervisors. Clear you browsers cache and retry
to log in to the supervisor.