I log into the site, go to the forums, try to open a thread and get the message that I'm not logged in. I'll log in, read the thread, try to reply or go back to the main page and I'll get the same message and have to log back in. I thought I was just going back too far to the log in page, but I'll be logged out trying to go from page 2 to page 3 in a thread.

Apologies for the insanely vague description! I can answer any questions if that helps. Thanks!