airport not configured

Suddenly I have a problem with Airport on my imac and hope someone can help me out. Two days ago, before the 10.6.2 update, my airport would disconnect from my network after waking the computer from sleep. The airport express is working fine, with its green light, and when I click the wifi symbol on the top window, the list of networks is no longer there and says "Airport: Not configured." When I go into my system preferences the Networks are present, and I can select mine. With that the computer is once again connected, but the "not configured" message remains under the wifi menu bar. After I put the computer to sleep and wake it again, it's disconnected and I have to go into System preferences again. This persists even after the OS update.
I even reset the Airport Express; but the problem persists.
I should mention I also have an older Ibook running Tiger and it works perfectly fine. The problem is restricted to the imac.

Any ideas?

The only thing different on my computer is that I installed VirusBarrier. Could this be messing with the wifi? Everything else on the computer works well. I can still get online, but there's obviously a problem here.