If you can, just as a final process of elimination, try accessing the CD on a system using an OS prior to Vista. I doubt if that's the problem, but it's just possible the burning software on your previous system did something odd with writing the multi-session disc, and Vista is being picky and not correctly seeing all the sessions on the CD.
If you do need to try for file recovery, a Google search will show a lot of options. Well known standards for example IsoBuster (shareware) and CDCheck (freeware). Most reputable download sites offer many possibilities, eg Majorgeeks:http://majorgeeks.com/downloads38.html