I have just backup my Genos, I have no error.
You don't have to remove your voice expansion or styles
In the Genos Reference Manual page 148:
Backup/Restore—Saving and Recalling All Data and Settings as a Single File
On page 2/2, you can back up all data saved in the User drive (except Expansion Voices/Styles) and all settings of the instrument to a USB flash drive as a single file named “Genos.bup.”
Before calling up the display, you need to make all desired settings on the instrument.
Touching [Backup] saves the backup file to the root directory of the USB flash drive. Touching [Restore] calls up the backup file and all data and settings are replaced.
If you want to include audio files, enter a checkmark to the “Include Audio files” beforehand.
NOTE
• Before using a USB flash drive, be sure to read “Connecting USB Devices” in the Owner’s Manual.
• The [USB TO DEVICE] terminal underneath the instrument cannot be used when backing up or restoring the data.
NOTE
• You can back up User data such as Voice, Song, Style, and Registration Memory by copying them individually to a USB flash drive on the File Selection display.
• If the total size of the target data for backup exceeds 3.9 GB (excluding Audio files), the backup function is not available. If this happens, back up the User data by copying the items individually.
NOTICE
Completing the backup/restore operation may take a few minutes. Do not turn off the power during backup or restoring. If you turn off the power during backup or restoring, data may be lost or damaged.