Tonight I updated the firmware on my Airport Extreme to version 7.4.1. When the device went to restart, I shut off the Airport Utility software and went about my business. I quickly found that my Airport was rendered completely useless by this update. After power cycling the router a few times and rebooting my Mac, I still had no luck. I could connect wirelessly but not access the internet. I could connect via the Airport Utility, but couldn't bring up the management screens because of an error "-5" saying something about not being able to read the configuration.

As it turns out, shutting off the Airport Utility during the middle of a firmware update will ruin the configuration on the router. If you update the configuration and cause it to restart, you can shut it down just fine. Doing an update to the firmware is a different case though. I ended up having to hold down the small unlabeled reset button on the back of the device for 5 seconds with it plugged in to reset the configuration on the device and now it is up and running again. Of course, I had to redo all my settings. Not too big a deal though.

After that, I updated my Airport Express to test my theory about shutting off the software. This time, I let it run all the way through before I shut it down and the firmware applied just fine and the device worked again right away.

You'll learn something new every day if you aren't careful.