I have been playing the MP for a long time and just recently hit this problem. The last few days on MP my game would freeze up and show 2 broken links suggesting I lost internet (which I have not, my wifi was around 60-70% when I checked it) and then it either kicks me out of the game or I show up dead 2 minutes later. Now I can not load MP at all, I get stuck on "error syncing levels" and if I feel like trying for 4 hours in a row (which sadly I have done) when it FINALLY gets to the welcome screen, MY WHOLE PS3 FREEZES. My controller doesnt work, NOTHING. And if I give up after the "error syncing levels" and try quitting the game, it shuts off my entire ps3 and controller. When I got kicked out of games I lost all of my earnings due to this.
So I googled the topic and found many people with the same issue, some suggesting its the disc. Well I bought a new disc and guess what, the problem was not fixed. ANY HELP would be appreciated because I am extremely frustrated at the fact I have spent so much time trying to fix this and now money and nothing works.