Connecting ADB using Wifi for non rooted device

I had the same problem.

I firstly connected my Android4.0.3 based device via USB and set the TCP/IP port to 5555

$ adb tcpip 5555

After that I disconnected USB connection and connected to device via WiFi IP and it worked.

$ adb kill-server
$ adb connect 192.168.2.5 
* daemon not running. starting it now on port 5037 *
* daemon started successfully *
connected to 192.168.2.5:5555