"File format not supported" randomly appears

I had posted in this thread before and my issue was solved with the 1.22 firmware update found here:

http://forums.sandisk.com/t5/SanDisk-Clip-Sport/SanDisk-Clip-Sport-Firmware-1-22-released/td-p/335935

Even if your player is new go to “Settings” >“System Settings”> “Info”, and verify your firmware “Version”.   If it is not 1.22 then update.

I hope that helps solve your problems!