I have 2 ipod nano's one will sync to itunes the second one says it won't sync because other applications are being used?

I have 2 ipod nano's (4th gen). I am able to sync one with itunes but the second one I get an error message saying that it cannot be ejected because files are in use by another application??? It won't automatically sync like the other one, and when I click the synce button it looks like its syncing for about 3 seconds then nothing.