I recently had this problem with one of my Clip Sports. I finally figured out my player (with an older Firmware) does NOT like the “m4a” files that I bought from the iTunes store. As soon as I deleted these files from my player (and micro SD card), everything went back to normal. Yay !!
After you rescue your device using the method suggested by drlucky, make sure you do not have any m4a files on your device.
