Can you play at least one music from your mp3 player? If yes, the file that you're trying to play when this message appears may be corrupted. Try having another copy of the music that you want to play on your mp3 player. If you can't play any music that you transferred, possible causes could be :
1. Your mp3 player was reformatted to another file system that is unrecognized by the mp3 player.
2. The flash memory of your mp3 player was bad
3. The songs that you're trying to transfer is not known by the player ( file types other than .mp3)