I`m having the same problem, tried to update firmware and now the amp is frozen, putting it in a safe mode doesn`t work.
I used M-Audio Uno midi interface, nevest drivers installed, tried on win 7 64, win 8.1 64, win 10, newest monkey installed, switching cables every way, using different usb ports,
nothing worked. I was in contact with Line6 support and they reccomended to send it back to seller for warranty repair. Very frustating, now i will be without amp for at least 4 weeks.