Three things to try or do:
1)Like Jenny100 said, if it is a slightly faulty DVD, you could try making a DVD copy if you can, sometimes by making a copy the marginal scratch in the original can be bypassed in the copy.
2)Try highlighting the Code, then hit Ctrl + C (to copy the code) and then go to the code screen and hit Ctrl + V (to paste the code) and see if that works. Do Not use the right-click to copy and then to paste, this tends to work less often then the good old fashion way of using the Key commands.
3)You could try contacting Iceberg Interactive, the producers of this game and see if they can help:http://www.iceberg-shop.com/contact-us.html