why is one playlist works but other playlist is empty

SanDisk MP3 players SanDisk® Clip Sport
11

Playlists don’t work for me either. Not a single one. I’ve created them with Mp3tag, VLC, manually. I’ve let mp3tag create a list from the files on the player. No go. No matter what I do, when I try to run the m3u I get “File format not supported”.