CDJ400 doesn't read usb (3.0)

Hi guys

When I put my USB in my CDJ400 it keeps on blinking and trying to read the USB, but it never recognizes any folders or files. I usually work with rekordbox but I also tried just putting some songs directly on the USB and the same problem occurs. I also already formatted it to FAT32 (I work with a macbook) but that doesn't change anything and I also tried another older USB that is not 3.0 and the same problem again. Can anybody help? I've never had this issue with other CDJ's.

Thanx alot!