My platform:
1.win7 x64 (client remote-viewer) ---> xp (guest vm) 
2.remote-viewer 2.0 
3.spice-gtk 0.29
4.libusb 1.0.20
5.usbclerk
I build spice-gtk and remote-viewer with usb redirection
 
Question:
1.I use command: "remote-viewer.exe spice.vv --spice-debug" to connect to xp
2.when i check the usb flash disk to redirect, it displayed error message like:
"Operation not supported or unimplemented on this platform[-12]"
3.I check the device manager and find the winusb driver is installed successfully by usbclerk .

debug info:
(remote-viewer.exe:28424): GSpice-DEBUG: channel-usbredir.c:329 usbredir-9:3: connecting usb channel 04988168
[14.420825] [00005d6c] libusb: debug [libusb_open] open 2.3
[14.420825] [00005d6c] libusb: debug [unsupported_open] unsupported API call for 'open' (unrecognized device driver)
[14.420825] [00005d6c] libusb: debug [libusb_open] open 2.3 returns -12


Test：
1.I stop usbclerk service to prevent it uninstalling winusb driver when i close remote-viewer
2.I restart remote-viewer like above, and now the winusb driver is ready,i check 
the usb flash disk , it redirect successfully! I try it some times ,check and uncheck it,all work well.
3.I use zadig to install winusb driver before i start remote-viewer like above , it also worked well
 
I wonder if it is a time question, the time that i install winusb driver.