This has happened to me before but not for so long and with such consistency.

ATM every time I click the "Offtopic" link I get the page to "Post a new topic here". The other links all work correctly. Sometimes this happens with other forum links, today it just seems to have picked the offtopic forum.

If I try long enough it will eventually let me back in for a while but then if I mark forums as read it does it again.