I have windows media player, the sansa shaker only uses mp3 files, nothing else at all. When I down load the songs they say mp3 but once they are on the memory card they say wma files. The sansa website says that some songs are overwritten with mp3 but that they are originally something else and that is why they won't play. It says it has to be a true mp3 file and I don't know how to tell if a song is a true mp3 file or not. I don't have any problem getting the songs to play on windows media player just the sansa shaker. Windows media player says it is converting the songs while I am putting them on the shaker but I guess it is not working.