Every now and again I can get in, but usually once it tells me I've logged in successfully, it pops back to the forum screen and still shows me as a guest, with the log in boxes at the top!!
I usually didn't have to log in every time, I guess my log-in was heald in a cookie or something. I don't doubt it's something associated with my computer, but I can't figure it out and it sure is frustration.