It's amazing how many people talk about things they know nothing about. Download Content is not going to make the disc suddenly not work (unless they overwrite the code that loads stuff on the disc). And if it did, getting a different disc for the same version of the game will not work. As was said before, you probably just need to let it finish loading, and make sure you're logged completely into Live.
Once again, if the disc worked BEFORE the DLC was downloaded, its not the disc that is the problem. If you scratched it after you bought it and didn't get any kind of insurance on it (like gamestop seems to love handing out so much), you're gonna need the money for a new disc, cause they wont take it back.
Anyone whom uses the pseudo-term "pwn", excepting this statement, is undeniably a n00b.
how do you access the dlc (corporate warfare and tera patrick)? Is it endgame missions?
They should be available after you break out of jail.
As for the game working before DLC thing, I've seen how fast a scratched disc can go bad. Anywhere between a couple of minutes to weeks, but if you constantly use it it tends to get worse faster. Especially if the system needs to check the disc for data often. SR2 is one of those games. Maybe it's a jump to check for that first, but it's a valid possibility.
Civilized men are more discourteous than savages they can be impolite without having their skulls split. Official Phantom Stranger of the C&GN