Sounds like it might be a corrupt disc? It might be an idea to contact Propellerheads tech support directly or to let your dealer who sold it to you know and try and exchange the disc or get a new disc sent to you.
Before doing that, try and repair permissions on your computer:
1. Applications/Utilities/Disk Utility
2. Select your internal HD and click [b]repair permissions[/b]
3. Restart your mac when it's finished.
Also, if possible try using another CD/DVD player connected to your mac to check if it's a fault with the mac's cd/dvd drive...
Let us know how you get on.