WLAN with NAS breaks

I have this FritzBox a week now in use.
The connection to the Internet works well, Internet phone, a connected Gigaset to the analog socket, works well.
Ethernet with my NAS works well, is faster than in my previous FritzBox 7170th

WLAN with my NAS breaks after about 4 minutes from transmission, the transmission just stops. In a normal file transfer on a laptop, the transfer window remains open, you wait and wait if the connection is resumed. After 15 minutes goes by one's patience and makes the window.
When Media Server of the NAS to your TV is the same. A abgepieltes song remains easily play under the middle hang. Man waits continues it, but in vain.
I've tried all the settings in the Fritz box. Currently there is on IPTV-optimized and full transfer without energy conservation.

I have been pleased with the 7170, just wanted a faster home network. Since the PCs, televisions, printers now understand all Gigabit Ethernet and Wi-Fi n and the 7170 just Fast Ethernet and wireless g dominated practically the bottleneck at the junction, I wanted a current Fritz box.

In 7390, incidentally, reported by the same wireless crashes, why I had chosen this 7570.