Y do some songs from my windows media play on 1 mp3 player but not a another 1?

i have windows media player 8..i tried the upgrade i dont like the new version..some of my songs will play on my husbands mp3 player but not on mine or off my sd card thru my phone..but all songs play thru the media player but reads error or licensed expired on my phone or mp3 player. why is this?