I have had this happen a couple of times. What works for me is to resync my ipod. I would remove all the music from my iPod and then reselect my music and resync it. That has always worked for me in the past.
I would imagine it's some sort of error(s) caused whilst syncing the iPod. I would try wiping the iPod and re-syncing everything, like NeoMac says. Use the 'Restore' function in the settings pane.