Hello Petr,
Thanks a lot for your reply. I sent you an e-mail with the requested files and some network traces that may help you.
Right after using the Avast report tool which indicated my version wasn't the latest one, I upgrade to the latest version of AVAST, reboot the PC, try again, but it's always the same...
I have usually only one network for internet on my PC but when I switch one of the Korg synthesizers on, a new network appears (UsbNcm Host Device or UsbNcm Host Device #2).
Hope this helps to solve the bug.
Thanks
Vince