I did a factory default reset of the airport express base station a couple of times and rescanned using the airport utility 5.6.1 and it still does not recognize it.
Please perform a Factory Default Reset again on the Express again as follows:
Power off he Express
Let it rest for a few minutes
Hold in the reset button first, and keep holding it in for another 9-10 seconds while you simultaneously plug the Express back in to power
Release the reset button after the hold period and alllow a full minute for the Express to restart
Temporarily, connect a spare Ethernet cable from your Mac to the AirPort Express
Now open AirPort Utiliy 5.6 and the Express should appear so that it can be reconfigured. You do not need AirPort Utility 5.6.1, but can use it if you want.
Once the Express has been configured, you can disconnect the Ethernet cable
If AirPort Utility still cannot "see" the Express, and you have tried the Factory Default Reset a few times, the Express is not going to work, and will need to be replaced