My 5th ten ipod menu does not play selected track - though it has loaded and is visible on the iPod.

I reformatted a 5th gen ipod and uploaded tracks from my Mac using manual management. All tracks are visible on the iPod, but some appear at the lowest level in the menu but then automatically flip back to the next highest menu level and will not play. All of the songs play on my Mac. And on the iPod menu selecting one track results in another track being played. Shuffle is not on. What gives?