The method StartHost() didn't work why ?

I have to do a multiplayer,In the New Unity Networking, with many options to be the avatar. So I had to customize the NetworkManager script, for turn it be able support more options of avatar. But now the method no works longer. here is the line of my code and what i can do to Solve this.

     public void StartGame()
     {
         NetworkManager.singleton.StartHost();
     }

thank you for your time.