I had the same problem with a similar model and fixed it by running checkdisk.
If you have a windows PC, plug in your mp3 and click on the start menu. Choose "run" and in the window type "chkdsk X:/F" (remove the quotes and change X to the drive letter of your mp3). This should remove any files that are corrupt and get you back to being able to add tracks and use the player as before.
angrybear, November 2008
