Some old CD-ROMS have problems reading copy protection.
Have you tried the game in another computer (with a hopefully) newer CD-ROM in it. This will let you know whether or not it's the CD-ROM.
You wouldn't happen to be playing from a backup copy would you? If so, does your original copy play fine?
If all else fails you can contact UbiSoft and seek support from them. They will probably just require your CD key and then they may be able to help you out.