CDJ-1000 MK3 folder search

Hello,

I'm a proud owner of a pair of cdj-1000's since yesterday. I'm still trying to 

figure everything out but there is one thing I'm struggling with. I want to be able to use the folder search for playing mp3's. I used a CD-RW and pressed the option 'use as a usb flash drive' to put the mp3's on there. But when i put the cd in the cdj it doesn't read it. When I burn a cd there is no problem at al.

Am I doing something wrong? Any help is appreciated.