I've been having this problem in BF3 and it seems to be down to a disc read error, as my PS3 won't load Battlefield Bad Company 2 at all.
I might be unique in this regard as it may be a server/software issue for the others that have posted here, but mine seems to be linked to my Blu Ray drive failing to read the disk as it goes "ker chunk.................ker chunk................ker chunk" very quietly - like it's trying to repeatedly read the same area on the disk, and the only way out of it is to manually turn off the system and restart - once the console is cold from a few hours of non-use the games seem to start and operate fine, at least for a little while. BFBC2 just dumps me out of the game like I've been kicked, and BF3 gives me the no weapons glitch and I end up running about like a total spanner getting shot at and letting other players rack up their score!! Not much fun if you're feeling competitive...hmph!
I bought my console second hand and it's worked fine for months and I've had lots of enjoyable gameplay from it, but I've no warranty so I'm going to have a go at cleaning the lenses and seeing if that works - if no joy, then I'm going to try replacing the laser unit and the mechanism for the disk loader (only about £20 from various parts places) and see if that works. If still no joy, I might just buy a SOR/faulty console on ebay with YLOD and switch out the bluray drive in that.
Failing all of the above I shall resign myself to a corner and sob gently into the broken remains of my main source of escapism, cursing Sony and their passion for planned obsolescense.
Wish me luck! I shall endeavour to report back here if it works so that if anyone else has this problem they can see if these solutions fix it.