Why does Messenger keep automatically signing me out?

I've looked through all the forums,

I've turned off MPOP

My internet has no problems with ANY OTHER program

I've scanned my computer for Malware over and over and there are no viruses

At a loss as to what's wrong and it's really annoying me now.

When I use a different connection I don't have this problem, so the internet is the only weak link, but it's running perfectly so I don't understand. I can't continue using that connection becasue that's just for uni - this problem will continue when I eventually return home. Any further suggestions?