It seems like your MBP has somehow lost authorization to that iPod. Have you always synced your iPod to this computer or maybe is that a new computer or something? Have you changed anything recently?
Is all of your music on your MBP and on your iPod or just on the iPod? If everything is on the MBP as well as the iPod then I'd just go and resync it with your MBP. If it is only on the iPod then I would download something like
IpodRip to download everything off your iPod and onto your MBP's iTunes, and then resync the iPod.