I had the exact same problem a few years ago, and I honestly forget how I fixed it. The folks at Lucasarts helped me get through all of it. You can contact them here:
Basically, they had me extract all the files from the disc manually onto my hard drive and install it in some weird way. Like I said, it's been years so I really don't remember how to specifically do it. I do know that it can be fixed though. Good luck.