mrpragay,
What format is your player at the moment Fat or Fat32?
Try building a new partition by removing any files from your player that you wish to keep, open the MP3 Player Disk Tool and go to the Partition Encrypt tab. Move the slider all the way right then back all the way left and press the start button.
This will create a new partiton on your player and quick format the drive, you should then be able to do a low level format