I've had this problem too. As I've read online you should uninstall the game utility data (not your game save) and reinstall it. If it doesn't work try it again and again until it does. Another solution that I've heard of was to uninstall the game data and not download the patch at all. I've tried both methods but it didn't work for me. However when I purchased the game for myself I bought the Uncharted Dual Pack that comes with Uncharted: Drakes Fortune and Uncharted 2 and tried it out to see if it froze or didn't load properly and so far it works fine, but I haven't tested it on multiplayer yet. One thing that I did notice when I borrowed my friends copy of Uncharted 2 was that it never froze until i started to play the multiplayer part which is why i'm not touching MP until I get my platinum trophy.
I am having a different problem with this level. I wanted to replay the game all the way through with out dieing or failing as this game puts it and was doing fine up to the tank battle. I managed to beat the tank boss no problem but, when I checked my stats once I gained control of Drake in the next chapter my enemies defeated streak ended. I went back to my last save played through level 20 again and did not die and yet again my stats showed that killing the tank ended my streak. I know this is an old game and people probably don't check these forums all that much but, I thought I would give it a try anyway.