I got a reply from tech support & this kinda worked for me - with the exception of the factory reset option ( I'm not sure if it worked or not because the VOL leds never lit up even after holding the 2 buttons down for over a minute...?)
In the end I deleted my Updater pgm, rebooted, reloaded & reinstalled everything ...
" I would suggest that you first try performing a factory reset on the AMPLIFi TT by holding the 'Tone' button and master volume knob down as you power on the AMPLIFi TT, continue to hold both of them down until you see the LED's around the master volume light up.
After the AMPLIFi TT has been factory reset turn it off once again, and press and hold both the 'Tone' and 'Tap' buttons down as you power up the AMPLIFi TT. To test that you have booted the AMPLIFi TT into 'Update mode' successfully, turn the master volume clockwise and it should scale fill with a red LED, continue to turn it clockwise and it will turn to a pink LED, continue turning it clockwise and it will turn to a white LED.
Once the AMPLIFi TT is successfully in 'Update mode' please try once again to then connect it to one of your available Windows computers USB ports. Once connected, try again to launch the Line 6 Updater application and apply the latest available firmware update for the AMPLIFi TT.
You can download the latest necessary driver version from the first link, and the latest version of the Line 6 Updater for Windows or OSX from the link below:
If you still encounter trouble attempting to apply the update, please try this entire process on all the available USB ports of the computers you are able to test with and report back with your results.