I seem to need to log in every 10 minutes or so.
Stop logging out then..?
Or take a hint.
But I've been asked to log in a few times too.
Happens to me too, seems to be when I am in a thread and use the link at the bottom of the page to go back to the sub-forum. If I simply go back a page from the log in screen and hit the home link, I am still logged in and all is good.