MacBook Air doesn't connect to AirPort Express

Hello people ,

I have a functioning wireless network with a Fritz box "7390" (living room) and a repeater "FRITZ! WLAN Repeater N / G" ( study) .

Now I have bought a Aiport Extreme (APE) , which should be connected as another device on the network that I mean music from mobile phone (iPhone 4S) , iPad (3) and my MacBook Air (MBA) on the investment in via Airplay can play the living room.

The establishment of the APE I have done over the iPhone and worked wonderfully. The playback of music via Airplay from the iPhone / iPad works well with no problems. The APE is found easily by means of the iOS app "Airport" from the iPhone / iPad.

Now to the problem :

From the MBA unfortunately can not connect to the APE are produced . Neither the APE is recognized by Airport Utility, nor can I over IP ( 192.168.2.xx >> does it normally ? ) Can access the APE . This dissipative I get in iTunes also displayed no Airplay icon , so playing music only on the MBA is possible.

Do you have any idea what I may still should consider ? Respectively . what can I do ?

Thank you!

OKraftDD

The details about the modules:

Airport Express (APE ) :

Model: AirPort Express 802.11n ( second generation)

Firmware: 7.6.4 ( up to date )

Fritz box (FB ) :

Model: 7390

Firmware: OS 5:50 FRITZ !

repeater :

Model: FRITZ WLAN Repeater N / G!

Firmware: 68.04.87

MacBook Air ( MBA) :

Model: MacBook Air 13 '' , in mid-2013

Operating System: OS X 10.8.5