Pink Screen on Scene loading

I am new to unity and having a frustrating issue I will do my best to explain!
I have created a little demo piece based on Windows Mixed reality headsets, the piece is made up of 3 scenes.
Scene 1 is essentially a scene selection screen, there is a canvas with 2 buttons each one calling the other scenes. Each scene can be built and runs perfectly in Visual Studio 2017... when I build all the scenes, the 1st scene will open... on pressing a button I am then presented with nothing but a pink screen (I can hear the audio playing in the background still) the buttons basically call this script.

using UnityEngine;
using UnityEngine.SceneManagement;
using System.Collections;
public class LoadOnClick : MonoBehaviour
{
public void LoadScene(int level)
{
SceneManager.LoadScene(level);
}
}

I know the scenes load as the music plays... just... big pink screen! Have tested scenes individually, even created a new project... if I test in Unity, it works fine... its only when building.
Any ideas... pointers... ANYTHING!