I have come to a very weird situation, where one of a dozens of macs (combination of iMacs, MacBooks and MBPs) doesn't list company wireless network. The affected machine list other networks in the same time (the other wifi network is a same type - WPA Personal)
I tried to turn on/off Airport, restart machine several times and remove "known networks" from the Airport Advanced list.
I faced the situation after a change of shared key on the Airport Base Station. The SSID is broadcasted and I'm able to connect to the network from the mentioned iMac using Other Networks option.