Backup of TES4: Oblivion won't install

[amg1984]

I made a copy of my oblivion dvd about a year ago when I noticed a crack appearing near the center of it. I believe I used alcohol 120% to make an ISO then nero to burn it. I remember back then the backup worked fine while alcohol was installed. I was using XP then, and the disc label was "NEEDS_RMPS".

Now I have windows 7 and I keep getting this "Please insert original disc and not a backup" message when I run the installer on the backup. I installed alcohol 120%, and now I get "Unable to authenticate original disc within time limit." In alcohol the option to enable RMPS Emulation is greyed out and so is everything in Extra Emulation. I also tried the Image Making Wizard(with the backup--the original disc has a large crack in it now), but it fails immediately with a disc read error.

So i'm posting this here hoping someone has some advice on what I can do to get this working. Would greatly appreciate it!