Help! 'Getting Access Denied' practically everywhere

I don't know what's going on, but following the Forum upgrade I'm having to reset my password daily just to log in, keep getting randomly logged out and I'm getting Access Denied messages all over the place when browsing the domain hosting the forum, though it's not affecting anything outside (e.g. Norton Account).

Is this because I may have been warned/banned (though I'm sure I'd have known if I was) or is it because of some bug in the forum?