im no expert but, i know from experience that when u rip music with mEDIA player they rip it to either WMA with "protection" so you can not play it on another computer. you must download some kind of licenses from microsoft just so u can play your music, YOU BOUGHT!!! (and copied)
it happend to me, a friend of mine wanted to send me a WMA music file and i could not play it cuz it was "protected" with licenses for use on her computer, i clicked on it and it asked me if i wanted to download licenses from microsoft and i said YES and only then i could play the music.
POINT IS THAT: if u want to avoid such hassle, just rip that Cd again, to mp3, download a program to do that, music match can rip cd's to mp3's free of charge. and if you want to keep the files Small, rip them to 96kbs bitrate or so, or maybe lower if u want. instead of the usual Cd quality 128kbs ....... IMO