I gave my wife a Vox for Christmas, and she opened while down at a friend's house. Got it onto the 'net via his WiFi and of course, got stuck at the Update failing problem.
Browsed the forums, and saw the advice to try a factory reset (Vox powered down, hold down vol+, power on, and keep holding the vol+ until a message appears that unit is resetting).
This worked perfectly, and the update applied perfectly.
Not sure there is any linkage but I can sure say that a factory reset SEEEMED in our case to let the upgrade happen.