KNetworkManager 3 problem on KDE 4

Hi guys! I have wireless connection at my place. When I use traditional method (with DHCP) on wireless network, everything seems to work fin, but when I switch to user controlled with network manager, I am online for about 1-2 minutes and then suddenly connection breaks. I need to click on network manager icon and select my WIFI network to obtain DHCP address again, and then again after approx. 2 minutes connection breaks again… and so on again.

What is the problem?