As reported in
Apple discussion forum, the recent Airport Extreme N firmware update to 7.4.1 has generated some problems. It affects stations purchased in USA but used in europe. Indeed, if channels 36, 40, 44 and 48 are available in europe, there 8 additional ones in USA, among them the channel 149. If the station selects the latest channel and is being used in Europe, no computer will be able to access it. Instead of reinstalling the previous firmware, you can simply push the Airport admin to manually select the correct 5 GHz European channel:
You simply need to press the "alt" key on the keyboard before selecting the drop-down menu of "channels" set by default on "automatic detection". You will need to get the station directly connected via Ethernet to the computer only during this quick channel definition procedure.
