Chk Files

You can delete the whole «found.000» folder. You need to make the «protected system files» visible to see it in the Windows Explorer.  The files therein are fragments found by Windows’ Checkdisk after a system crash or a broken USB connection during file transfer. I have no idea how it’s possible to get such an amount of .CHK files at once, though. You may want to run Checkdisk once more to ckeck the integrity of the music files on the player.