after several times of being logged out
I'm AWARE that this happens to some folk, but it is the settings on there computer not the server. If they login with the same details on another computer it works fine.

Peter, they cannot be LOGGED OUT if they can't connect with the server

Problem is usually;
Cookie settings
Corrupt cookie
Firewall
AV needs running
Spyware needs running

Problem solved in 99.99% cases once those are done.