keyword void cannot be used in this context

Hello

        Actually I am develop the chat application using MangoChat Application but some errors are come in that code .

 error line : 

ChatControl.StartSession();

void ChatControl.StartSession(string username);

   Plz let me know how to solve that error...

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using ASPNETChatControl;


namespace SampleChatProject
{
    public partial class _Default : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            ChatControl.StartSession();

            void ChatControl.StartSession(string username);

            void ChatControl.StartSession(string username, string ChatPhotoName);

            public static void StartSession(string userId, string username, string ChatPhotoName);

        }
    }

}