When I sync up my iPhone 4 everything syncs fine except for music. Podcasts, playlists, apps, notes, contacts etc. All of that is fine. But once it gets to music suddenly iTunes can't read or write to the disk. Videos aren't syncing either, but I think that's because they sync after the music does. The playlists are empty. I'm utterly confused. The error message simply says that it can't read or write to the disk. Anyone have any ideas?