I got using these steps:
Hard reset
A hard reset removes current settings from the base station. You must then connect to the base station using the AirPort Admin Utility and upload AirPort 2.0 or later software to return the base station to its default settings. A base station in a hard reset mode is only accessible through the LAN port, not via wireless connections.
To perform a hard reset:
- Unplug the power adapter.
- Press and hold the reset button.
- Plug in the power adapter.
- Release the reset button after at least two seconds total have elapsed (including the time required to plug in the power adapter while keeping the reset button depressed).
The middle LED blinks at a rate of once every second while in hard reset mode.
He said to hold two seconds including call on force rather than thirty seconds to say Apple's official procedures.
The complete procedure is at this site:
http://davidthegeek.blogspot.com.br/2007/08/resetting-airport-base-station-dual. html
Nothing I read about the procedure to recover the password were valid, only this was the correct one.