Q: Why do I get "...could not copy to ipod due to an unknown error (-50)"? All purchases beyond that song will not sync.

I have been purchasing music from Itunes and Amazon for years, all synced without prob. I purchased music in Aug from Amazon, download fine onto ITunes. Ipod syncing stops at same song with: "ITunes could not copy ...onto ipod because an unknown error occurred. (-50)"

Music purchased on ITUNES after will not sync onto device now or since. I would like to perm, completely

delete this prob song or find another solution.