USB playlist not recognisable CDJ850

G'day Pioneer, 

So i have two 16G sandisk ultra USB 3.0 flash drives which i use when playing at a bar that has CDJ850's. Both are backwards compatible and both are FAT32 formatted. However 1 of the flash drive is displaying "Playlist not recognised' ( can't remember the exact wording, but it was definitely unable to read my playlist or navigate past this to view any music at all ). I honestly have no idea what it could be, one works the other ...

Do i need to purchase another USB or is there something i can try ?

Look forward to hearing back about the issue.

Sam