First steps in Photon doing TrueSync tutorial - stucked right at the beginning

Hi, i've just started using Photon to modify my Unity Game into a MultiPlayer Game. Since it is a game which uses a lot of physics calculations I think TrueSync is my best option. To get familiar with Photon and TrueSync I'm doing this tutorial:

I followed every step very closely: I imported TrueSync from the Unity Asset Store. I created a TrueSync AppId and added to the PhotonServerSettings. I switched on Auto-Join Lobby and chose Best Region, Everything. I created a Menu and a Game Scene in a new folder called Tutorial and added both scenes to the build setting (1.Menu, 2. Game). I added the following code to a script called "TutorialMenu.cs" and attached it to the main camera in the Menu Scene:
using UnityEngine;
using System.Collections;

public class TutorialMenu : Photon.PunBehaviour {

	// Use this for initialization
	void Start () 
		PhotonNetwork.ConnectUsingSettings ("v1.0");

	public override void OnJoinedLobby()
		Debug.Log ("Lobby Joined");
		PhotonNetwork.JoinOrCreateRoom ("room1", null, null);

	void OnGUI() {
		GUI.Label (new Rect(10, 10, 100, 30), "players: " + PhotonNetwork.playerList.Length);

		if (PhotonNetwork.isMasterClient && GUI.Button (new Rect (10, 40, 100, 30), "start")) {
			PhotonNetwork.automaticallySyncScene = true;
			PhotonNetwork.LoadLevel ("Tutorial/Game");

When I make a standalone build and let another game instance run from the unity editor, on both instances the other player joining the menu scene is recognized (Player Nr going up two 2). But when I press Start on the Master-Client only on the Master-CLient Instance the Game Scene is loaded. I'm sure I'm missing something very simple, but these are my first steps in PUN. Thanks for any help.
btw, I'm using Unity 5.4.3 on a Mac