An error occurred while updating the firmware. How do I figure out what the issue is?

The AirPort Utility checks http://apsu.apple.com/version.xml for firmware updates. When updating the device's firmware, both the base binary and a signature file are downloaded to the host. The firmware update is verified before it is sent to the device. It is verified again on the device, then unpacked and written to flash storage. The files are downloaded to : ~/Library/Application Support/Apple/AirPort/Firmware/

During the "Preparing Update..." stage, the firmware files are being verified. Next you would you see the "Updating Firmware.." message. Obviously something went wrong at this point.

Some things you can try:

• If not already, connect your Mac directly to the base station by Ethernet.
• Verify that your network is configured for, at least, "IPv6 Link-local." If you are still able to access the base station, you would verify and set this using the AirPort Utility, as follows:
  • Run the AirPort Utility, select the base station, and then, select Edit.
  • Select the Internet tab.
  • Select Internet Options...
  • Verify that the Configure IPv6 option is set to: Link-local only

You should get that error message after your download of new firmware is complete. After you see the error code, try disconnecting the Airport from the power source, wait a beat or two and then reconnect the power. with luck, your blinking airport light should turn bright green within a minute or two