Hi Millie,
I don't think it's your CDs.... I have the same problem, where all my BodyStep releases were skipping on track 6 on my iPod. I have 4 BodyStep releases since I trained, and I purchased 4 back releases, so I know it couldn't be all 8 CDs! I tried burning a copy on my computer, and when I uploaded, it still skipped on track 6. When I burned a copy on someone else's computer, the copy uploaded to my iPod just fine. I think it's either my CD-rom drive is damaged, or that my computer is older than my iPod so the technology doesn't correspond.
Try using a friend's computer, maybe someone who has a newer computer than your own, or have another instructor burn you a copy and see what happens. Good luck!