Audiobook not playing through

I have two audiobooks purchased from iTunes: Kathy Griffin and Paula Deen. I bought Paula a few years ago and have listened to it through to the end. Kathy's book, I read in paperback, so I purchased it a few months ago and tried to listen to it today.

I'm having an odd issue with them. I cannot listen past a certain point, with Kathy, about 40 minutes into a 6 hour audio. I first noticed it while playing it in my iPod classic. I then played the file in iTunes, the latest version, and when I try to advance to the end of the audiobook, it skips to the next book entirely.

Anyone else having this issue? Any suggestions with whom at Apple I can take this up with?

Thanks a lot.