Q: When I control-click (or right click for the Windows folks) my iPod in iTunes 4.8, there is an option called “Reset Warnings.” What does this mean?
A: If iTunes cannot find one or more of your songs when updating your iPod, it displays a message:
Some of the songs in the iTunes music library, including the song “Song Name”, were not copied to the iPod “iPod Name”, because they could not be found.
This dialog has a “Do not warn me again” option that you can check to turn it off. If you select Reset Warnings from the contextual menu, iTunes nullifies this choice; it’s as though you unchecked the “Do not warn me again” checkbox. iTunes will then tell you if it cannot find any of your songs.