USB Passthrough on 8600 not working

I have been using the great new feature for USB Passthrough for several months now quite successfully controlling my rotor with PstRotator through my 6600M radio.

But I migrated to my new 8600 this weekend, and I cannot seem to get this to work now.

I had backed up all my profiles from the 6600M and imported them into the 8600, and everything came across just fine.

The COM port for passthrough is still in place, as well as the USB cables config, and the new radio sees the cable like normal.

I have done the obvious, of deleting the usb passthrough port in CAT, and unplugged the usb cable from the radio and removed the config for the USB cable. Powered down and removed power from the radio. etc…

Then re-added the CAT port and USB Cables config after the cable was plugged back in, but it still doesn't work.

When I start up PstRotator, the CAT does indeed show the application there as being used, but when I turn on the log on the USB Cables area, it's showing every command being transmitted from PstRotator, but still no control of the rotor.

Just to ensure nothing had changed with the rotor, I reconneded things back to the 6600M, and the rotor control is working perfectly as before.

Any thoughts or ideas I may have missed?

Many thanks, Walter/K5WH