Why doesnt a CD Ive Burned PLay on My Ghetto blaster?

I am currently sing RealMusic (Frostwire) and the songs I have downloaded/burned onto a CD (for my own personal use) - the CD doesnt work in my ghetto blaster yet it works fine on Hi Fi and computer, why is this? (By the way I use my Ghetto Blaster when I am in the bath - outside the door!)