+1 for a fix. I don't have any saves from before the Zaeed mission. :-(
EDIT: HA! FIXED!
This seems to happen if you let someone else use your computer, log in with their acccount. and install DLC for which you are not authorized so they could use it. When you switch it back to your account, initially the only side effect is that it complains you're not authorized, but otherwise it seems like no big deal. Then this happens. If you delete or move the appropriate folders from C:\\Program Files (x86)\\Mass Effect 2\\BioGame\\DLC (this takes a little guesswork) the saves work again.
If your PITA friend wants to mess with your stuff again, tell him/her to find new friends.
Hope this helps.
EDIT X2: IAMRandommer's below is probably better. Note the directory mentioned in that post is if yours is the Steam version, while mine is if yours is not. (Obviously.)
Edited by Honorable Reverend, 23 September 2010 - 03:05 AM.