I just had the same problem!!!! I've been playing Generations for a week or two with no major problems (ok, some annoying bugs as usual but nothing terrible) and now I tried to start the game but the launcher won't read my disk. I remember once having the same issue with The Sims 2 and I fixed it by starting the game directly from some folder... but I don't remember exactly how. I'm going to make some research.
And I was so happy that my game had not crashed like when I installed Ambitions and Late Night lol.
EDIT: I fixed it! maybe this will work, Susan:
I actually think the problem was with my launcher not reading the disk, not the disk itself... which makes sense, since my launcher got broken with a patch some time ago. It just closed itself showing an error everytime I clicked the "play" button but didn't cause much trouble, but maybe now it got worse.
Anyway, as I said before, I remembered having fixed a similar issue by going to C: and opening some folder, so I looked in the forum and found this thread by Pam:
http://www.carls-sims-3-forum.com/index.php/topic,1186.0.html. It sounded familiar to me, so I followed those instructions and now my game is happily loading.... and guess what! I think it actually got fixed forever! Some Sims 3 strange setup started itself, then failed, gave me an error message... and now the Sims logo, which was blank ond my E: folder, is showing up again. I don't have the least idea what this means or why it happened, but I'm happy it wasn't anything worse.
Maybe you should try those instructions first and see what happens. I'm not an expert here, and I may be wrong, but unless you damaged the disk yourself (like by making it wet or something) I doubt it got damaged out of the blue... so it's very possible (I think) that the problem is caused by the launcher. Good luck