cdj 850 dont recognise the usb library

i have problems using usb flash with record box playlists on a cdj850 , the usb is formatted in fat32 and they have the latest firmware. 

the error is : Library not recognised 

Please help me, the cdj's are brand new ! I also tried to put songs on usb without record box and it said : Library not responding 

what should i do? 

thank you

Codrin