AirPort Utility

OK i'm going to shorten this up as much as i can and get down to the facts. I am running a 17" MacBook Pro (Mid 2009) with the newly released 10.8 Mountain Lion installed. I upgraded from 10.6.8 Snow Leopard. While i was on Snow Leopard, i had my wireless setup as follows.

Time Capsule as my main base station hooked to a cable modem.

AirPort Express (802.11g)

Everything continued to work even after the upgrade to Mountain Lion. I was still able to print to my AirPort Express (secondary base station). The whole network was established beforehand.

However, i recently had to have my mac in for repairs, and during the course of the absense of my mac, and getting it back again - it messed up my wireless network and my Express wasn't working anymore.

I tried to go through the AirPort Utility app (version 6.1 on Mountain Lion). When i tried to configure it, it gave me this error message: This version of AirPort Utility doesn't support this base station. Use AirPort Utility 5.6 to configure or manage this base station. AirPort Utility 5.6 is available at this...blah blah (page that did not have a download link to version 5.6.)

So i hunted it down and found it to download off the Apple Website - however, it cannot be installed on Mountain Lion.

So how is it that it was working before i had it in the shop, and now that i got it back, i can no longer configure it? Why would it even continue to work after the upgrade to Mountain Lion if it wasn't going to allow me to re-configure it later?