Macintouch Wireless Networking (Part 26): "Jason Froikin: AirPort Extreme and AirPort Express attached USB printers will often change ID's after a new firmware upgrade, even if you didn't rename the printer. It won't work again until you delete it from the Printer Setup Utility on your Mac and add it again via Rendezvous.
If you had the printer attached and turned on, sometimes the printer will get erroneous codes during the upgrade and get stuck. Turn off and detach the printer, restart the AirPort and, and reattach the printer. Then follow the instruction above."