I did patch an Alpha 100 yesterday and had no issues, I used the cable that were included in the Gps-kit.
and used an USB3 hub.

Have u tried a different cable? fully charged the device? ensured ure in preboot mode?
=======================
just patched second Alpha 100.

worked fine this time aswell.

Just abit timing required when plugging in cable in gps, and releasing the power button on gps. to be able to get in preboot mode.

correct method is:

start updater on PC, and choose usb mode.

-hold down power button on gps and make sure no cable is attached to gps.

-keep holding button until garmin logo appears, plug in usb cable while still holding powerbutton.

-Updater should now recognize gps and you can release powerbutton.

-flash the firmware.

-wait for 100 % and then you can disconnect gps, and finally restart it.



if your only getting to screen calibration on gps you just need powerdown gps and retry the steps above.