Script not working

Hi guys i've been working on a multiplayer game on android and have been following this useful tutorial from thefacegrabber on youtube but after i followed everything he did(twice) I still get the same problem.When he presses the start button it goes like to another level but when i press the start button it gives me this error. You may not be connected when initializing security layer. UnityEngine.Network:InitializeSecurity() NetworkManager:StartServer(String, Int32) (at Assets/Scripts/Network/NetworkManager.cs:23) Menu:Host() (at Assets/Scripts/Network/Menu.cs:48) Menu:OnGUI() (at Assets/Scripts/Network/Menu.cs:30). Here's my menu script.

 using UnityEngine; 
 using System.Collections;
 
 public class Menu : MonoBehaviour {
     
     private string CurMenu;
     public string Name;
     public string MatchName;
     public int Players;
     // Use this for initialization
     void Start () {
         CurMenu = "Main";
         Name = PlayerPrefs.GetString("PlayerName");
     }
     
     // Update is called once per frame
     void Update () {
         
     }
     
     void ToMenu(string menu){
         CurMenu = menu;
     }
     void OnGUI(){
         if (CurMenu == "Main")
             Main();
         if (CurMenu == "Host")
             Host();
         if (CurMenu == "Lobby")
             Host();
     }
     private void Main(){
         //if (GUI.Button(new Rect (0, 0, 128, 32), "Host A Match")) {
         // ToMenu ("Host");
         //}
         if(GUI.Button(new Rect(0,0,128,32),"Host a match")){
             ToMenu("Host");
             Name = GUI.TextField (new Rect (130, 0, 128, 32), Name);
             if (GUI.Button(new Rect (260, 0, 128, 32), "Save")) {
                 PlayerPrefs.SetString ("PlayerName", Name);
                 
             }
         }
     }
     
     private void Host(){
         if(GUI.Button(new Rect(0,0,128,32),"Start")){
             NetworkManager.Instance.StartServer(MatchName,Players);
             ToMenu("Lobby");
         }
         
         if(GUI.Button(new Rect(0,33,128,32),"Back")){
             ToMenu("Main");
         }
         MatchName = GUI.TextField(new Rect(130,0,128,32),MatchName);
         GUI.Label(new Rect(260,0,128,32),"Match name");
         Players = Mathf.Clamp(Players,0,8);
         GUI.Label(new Rect(260,32,128,32),"Max Players");
         if (GUI.Button (new Rect (145, 32, 32, 32),"+"))
             Players ++;
         GUI.Label (new Rect (192, 33, 64, 32), Players.ToString());
         if (GUI.Button (new Rect (215, 33, 32, 32),"-"))
             Players --;
     }
     
     private void Lobby(){
         if(GUI.Button(new Rect(Screen.width - 128,Screen.height - 64,128,32),"Start")){
             
         }
         
         if(GUI.Button(new Rect(Screen.width - 128,Screen.height - 32,128,32),"Back")){
             ToMenu("Host");
         }
     }
     private void MatchList()
     {
         if (GUI.Button(new Rect(0,33,128,32), "Refresh"))
         {
             MasterServer.PollHostList();
         }
         if (GUI.Button(new Rect(0,33,128,32), "Back"))
         {
             ToMenu ("Main");
         }
         GUILayout.BeginArea(new Rect(Screen.width/ 2, 0, Screen.width / 2, Screen.height), "Server List");
         foreach (HostData hd in MasterServer.PollHostList())
         {
             GUILayout.BeginHorizontal();
             GUILayout.Label(hd.gameName);
             if(GUILayout.Button ("Connect"))
             {
                 Network.Connect(hd);
                 ToMenu("Lobby");
             }
             GUILayout.EndHorizontal();
         }
         GUILayout.EndArea();
     }
 }

NetworkManager Script

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 
 public class NetworkManager : MonoBehaviour {
     public string PlayerName;
     public string MatchName;
     public static NetworkManager Instance;
     public List<Player>PLayerList = new List<Player>();
 
     // Use this for initialization
     void Start () {
         Instance = this;
         DontDestroyOnLoad(gameObject);
     }
     
     // Update is called once per frame
     void Update () {
     
     }
 
     public void StartServer(string ServerName, int MaxPlayers){
         Network.InitializeSecurity ();
         Network.InitializeServer (MaxPlayers,25565,true);
         MasterServer.RegisterHost ("Tut", ServerName,"");
 
         Debug.Log("Started Server");
     }
 }
 
 [System.Serializable]
 public class Player{
     public string PlayerName;
 
 }

I posted on his youtube channel but no response.If anyone knows why this is happening wplease respond