WIFI-Shield, only sporadic connects(10%) to arduino-webserver

Hi all,
I use arduino uno and the wifi-shield, it works out of the box with the samples for detecting existing wlans and calling other servers (e.g. google). If i try to connect the arduino server it works in only 10% of all trials.
I tried the WifiWebServer-sketch.
I found also this thread:

but i don't understand, how to change the sketch to get it work all the time.
I updated also the firmware for the wifi-shield (master from github) successfully,after that i saw the first successful connect.
If there is a successful connect, then come 2-10 further connects and then the server hangs.

What to do?

Is there a possibility to request the firmware-version from the wifi-shield?

best regards
barman