Hello guys!
In case you did not find a solution, after trying everything I found on here and failed, I did this and worked:
On your PC (mine is running win 10),
Download and install Line6 Driver2 from the official Line6 download page ,
Download and install the Line6 Updater,
While pressing A and C buttons, power on your unit ( works on amplifi fx100),
Plug it in your pc, via an USB cable,
Run the updater utility, log in, and it should recognize your unit.
Then click on the device you want to update, select the latest firmware and press update.
After a few moments, your amplifi should start and run like it sholud.
Hope it helps!
