Play a game that isn't so blatantly historically inaccurate. Still insist on playing it? I would suggest hard booting your system and trying again. Sometimes that is all it takes to fix little errors like that. If that doesn't work, you may have a faulty disc. You can also check the Ubisoft Support Page and see if they have a fix for that specific problem.
Take it back and ask for a new disk, or take the disk to somewhere that does DVD/CD cleaning and scatch polishing.
Basically your reader can't access the CAB files (in your case that specific CAB file) on the disk to decompress and extract it.
If you have an older slower DVD reader/writer sometimes they can have trouble reading disk is there is no visable sign of scratch's