Ewww. That's not good bud! You have a few options.
EDIT: I just woke up, lol I gave you all these options and I think all you need to do is delete your MW2 game data and then just re-download the patch.
1. If you have a second PS3 or if a friend has a PS3 that's still on 3.55 or 3.41 then you can do a data transfer to your PS3.
2. You can take the risk and use
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to downgrade back to 3.55 CFW and fix it, but it is risky.
3. You can wait until a new 3.56 CFW is out but that might be a while and I really think SONY has some secret stuff going on in the new 3.56 that will make it much more difficult to get CFW after you've updated, or they have more remote access options to see it and perma ban your PS3 from the PSN.
I wish you luck, those are the only options I can think of for right now. Me personally if you don't have a way to do option 1, I would do option 2.