Hi Dennie. I had the same problem. I find that “transcend jetflash 790” usb drives work just fine. There will be others that work too, but the jetflash produce replicable results. Maybe you need to format them FAT32 before use (even though they come pre-formatted).
there’s some more information here: https://community.allen-heath.com/forums/topic/usb-key-for-me-1
Hope this helps.
