Sorry, I forget we are multinational!

I wonder if there's something about the way the software is trying to communicate.

I remember the Yamaha "To host" serial cable installed itself to look like another Midi device; is this also the case for the USB drivers?

If it is the case, have you now got two USB "Midi" ports both from Yamaha which are getting in each others way - I'd remove one of them.

You may have to then go back into the software and re-assign their midi outputs and inputs to be the USB "midi" device.

Hope this helps!