What have you changed ? Did you do a reinstall ? Did you add another hard disk/cd rom drive/dvdrom ? If you suddenly get such a message and you didn't change anything, I think either your cd or the drive you put it in is broken. I'd try to find out what's the problem, especially since for a nocd, you really have to copy the contents of the Audio folder on your hard disk too, otherwise you'll have almost no sound in the game. Here's a bunch of
cracks anyway, don't forget to update to v1.1.