Luckily everything is supposed to be steadied out on Friday. Including the problem with joining a party. If you are having this problem what you need to do is..... Get your friend to send you an invite (do not accept it at this point), log out of the playstation network, log back in, go to the "play online" menu in the game then go to your xmb and accept the invite, should put you right in the party. My friends and I have been doing this and it has worked every time.
What the hell does that have to do with this thread?