Disklavier

Any help with this issue appreciated.

I purchased a portable USB disk drive of about 300 Gb and formatted it to FAT 32 using the Apple OSX Disk Utility program.  Both my Apple computer and a Windows 7 Laptop I have indicate that my portable drive is formatted FAT 32, required to use the backup function.

I have a Mark IV running version 3.0 of the software.  I found the backup function under "System", and all appears to proceed normally until I get the error message quoted above "No USB medium".  I have plugged the drive directly into the USB port on the main computer under the piano.

Any suggestions regarding what I am doing wrong?  I suspect there may be a problem with the size of the "Partitions" on the disk drive; they may be too large.  I have used the disk drive in other applications, and it works fine.

Thanks.

Steve