[SOLVED] Borderlands - General Protection Fault??!?

So I bought borderlands this weekend, and I played single player for a few hours perfectly. Then my friend decided to get it and he started playing and we were going to play together, however i could not log in to play online after fiddling around it finally worked but now whenever I did get in his game i would get a general protection fault error.

I just kept joining and then finally it did it again, so i searched for some fixes, opened some ports etc. nothing, however now when I even start the game I get a GPF error, i have tried messing with core affinity, reinstalled physX, rolled back gpu drivers... still nothing.

I would really like to play this game with my friend, or at all even. Any ideas?