Airport Firmware Update 7.4.1 : NOT UPDATED!
5 days ago was released by Apple firmware update 7.4.1 for devices Airport.
in this case, has been updated an extreme n gigabit.
Now the problems started: He decided that the only way was to work in 802.11n mode NOT COMPATIBLE b / g, a 5ghz.
While this may be fine for the Mac Book Pro, you can not say the same for the older devices.
Using other modes wifi, the signal was not displayed, or was connected for a few seconds then go out.
The only solution is to use the Airport Utility to reload the old firmware 7.3.1 (right click on the device, LOAD FIRMWARE), and everything will return to normal.
The problem is confirmed by other users with Time Capsule, more information THIS LINK
The conclusion? DO NOT upgrade your firmware to the device Airport 7.4.1 !!!!