You can force a user to be logged out by running this query in PHPMyAdmin:
UPDATE mybb_users SET loginkey='' WHERE uid=x;
Replace x with the person's uid.
Thanks very much buddy you are awesome! It's a bit strange cause it doesn't happen all the time juts sometimes!
Guys I am sorry to bother you but this issue persists!
The user show online on postbit when I go to profile it shows offline.
I have noticed that despite the fact it shows offline Last Visit: time keeps increasing on it's own!
I mean its one minute behind the Current time:
When I refresh the page after 5 min it had advanced 5 min I mean it never stops.