Have you tried using a different USB cable and USB port? Try that. If that doesn't help, try restarting your system with the AP connected, and then open up AP Manager.
I have an AP for my MINI so I hope when you try to update, it doesn't get stuck on an "Updating..." screen, because then you'll have to send it back to AP, which I've had to do twice. Hopefully this won't be an issue for you.