WWW problems on android

I have t$$anonymous$$s code:

 public tk2dTextMesh debugMessage;
 
 IEnumerator CoExecute()
 {
     string data = "some data";
     WWW req = new WWW(serverName + "/?" + data);
     yield return req;
     
     if (!string.IsNullOrEmpty(req.text))
         debugMessage.text = req.text;
     else
         debugMessage.text = "No result??";
 
     result = JsonMapper.ToObject<MyClass>(req.text);
     if (!string.IsNullOrEmpty(result.error))
     {
         debugMessage.text = result.error;
     }
 }

It works fine in the editor but after building on android the debugMessage shows "No result??" w$$anonymous$$ch means it's not an error in the request.

Note: debugMessage is a text mesh from 2DToolkit asset.