Synchronize to continue your music subscription
The "synchronize files to continue" is annoying, and you are likely to get it again. If the music files on your player came from Rhapsody, the short-term solution is to re-synch the files through Rhapsody itself. If your subscription to Rhapsody, Overdrive, etc. ever expires, you will also get this message. The only long-term way around this problem is to only load songs that are in mp3 format (Rhapsody has an Mp3-Only subscription, which is different from its regular subscription; Limewire is another choice - but it is prone to have viruses, and some ISPs will cut off your broadband if you use the service). If you wanted to erase all songs and start over from scratch, you could update the firmware on the player - it will have the side effect of erasing everything on the player.
-Tha Mp3 Doctor