Have you tried to tell to MBA to forget your Network and then change its name ?
You can even try to remove all passwords for the time to connect it the first time.
Other problem which happended to me was a MAC address filter set up with incorrect data, but this should not be your case since it connected before...
It sounds as if you already accomplished most of what this says
but read it again to determine if there was something you missed. After that, call AppleCare since you have done everything any reasonable person should have done.
At this point I am reinstalling Lion. I did what apple/another person said to do by deleting the system config file, shutting down and pressing certain keys (I'm so flustered I can't remember what they were) until it prompted me to "reinstall utilities." I am new to Mac so I have no idea which option to choose... If I reinstall a new version am I losing everything on my computer??