I had the same problem and still don't know why it happens, but had a reasonably simple (but kind of stupid) fix - rather than repeating it, let me just refer you to the appropriate thread: https://discussions.apple.com/message/18123183#18123183
I have the latest Itunes and a IPOD CLASSIC updated.
Some songs i can play in itunes (MP3 CDRip 320 KBS) won't play in the ipod.
I don't know how to fix this problem.
I restored the ipod from the itunes and sync again, but the problem persist.
The sogs are Skipped when i try to play.
I find a fix for this problem: sync the music with mediamonkey.
ALL songs can be played in the ipod after sync with mediamonkey.
Is very strange this problem, maybe itunes generate this problem, because after aync with itunes many songs are skiped and won't play, but with mediamonkey sync the problem is solved.