Session problem

Hi,

I have a website that is accessed by authenticated user through login
page

The problem is that when the electricity goes off or the user do not
log off properly, the users are not able to log in again.

For this purpose, i have to kill their sessions that is maintained at
the server, but despite the fact that the sessions are killed, the
users are still not able to log in. The message comes (You are already
logged in)

I have also generated a script that removes the caches for the
corresponding users on the server on every page click, but still that
is not working.

Can anyone tell me what is going on and the solution for it

Regards.