Don,
I just copied folders from my computer of Roland styles and many folders of various midi files and mp3 files onto a 2 or 4 gb usb drive and they showed up perfectly when I pushed the usb switch on the BK7m. As stated earlier make sure you are not using a drive that might have drive exclusive information. Make sure you remove any proprietary information from your drive. I have a utility program on my computer which completely erases everything off a usb drive to make it completely clean. I received 2 more BK7m modules today which were pre sold to Synthzone guys and I made drives for one of them and it read perfectly as well.