When i try to join one of my friends in multiplayer my game freezes at the loading screen for a mission....but only on multiplayer if i start a mission offline it goes through. There are no scratches on my disk its is like right out of the case. Im getting annoyed all i wanna do is play online with my friends i payed good money for this game.

It's either a faulty disc which should be returned, or your console is dusty/overheating/has a rather full HDD. Mine certainly doesn't do it.

EDIT: It happened to me. I had a new friend in my list, he invited me to a game yesterday but I was already grouped up, so I figured I'd hop into his games today. Well I followed him into 3 matches, one of them twice, and froze in each one. Thing is, I would be able to play for a few minutes, but then out of nowhere mid-game the loading screen with the art for the level would pop up. There wouldn't be any text, the spinny thing would spin for a couple seconds but then the whole thing would freeze.

Happened 4 times in a row. I joined other people's games just fine, even started some online matches of my own, but it seemed like just his games were freezing me. If you're only trying to join one person and this is happening, might just be that something about that person hosting doesn't agree with your connection and overloads the system.