Have you made sure that you have cookies enabled in your browser?
Are you using an AOL browser. Please see the following technical response from JelSoft:
They just need to tick the "Remember Me" box, for security reasons we do host matching. Unfortunately with AOL they randomly change the host between requests resulting in the session being destroyed.
in 3.5 and below we had the "Remember Me" box checked by default, this was removed due to security concerns as it required the extra step to logout.
Probably not this but I had the same problem for a bit and discovered my clock was set to the wrong year.
i didnt have a chance to have a look at my cookie settings i think i shall remote my pc now and take a look.
any other ideas about what the problem is would be really nice
thanks for your help so far