You might try this. Worked for me.
The guitar player in the band I'm working with brought me a sandisk 16 gig stick. I formatted it & tried to record from the usb out on my x32. No get. Today, after talking with a computer guru friend of mine, he suggested that I should format using "disc management" on my computer as a "regular" formatting does not always completely remove everything installed on usb drives, even though they show that they are clean. I did this & now the drive works perfectly. I don't know that this will work with all USB drives, but you might give it a shot. Here is a link from the Sandisk site on performing said format....
Formatting a drive or device using Disk Management
The guitar player in the band I'm working with brought me a sandisk 16 gig stick. I formatted it & tried to record from the usb out on my x32. No get. Today, after talking with a computer guru friend of mine, he suggested that I should format using "disc management" on my computer as a "regular" formatting does not always completely remove everything installed on usb drives, even though they show that they are clean. I did this & now the drive works perfectly. I don't know that this will work with all USB drives, but you might give it a shot. Here is a link from the Sandisk site on performing said format....
Formatting a drive or device using Disk Management