Problem using OnStartServer() for multiplayer networked game (only works if the 'Host' is in Editor)

Hello everyone I am making a football game which you control one player from the team. It will connect 11v11 players per server (using a "Host" acting as server and client, and other clients connecting to them)

I believe I have followed the examples and information provided by Unity to the letter, but I can't seem to get it working properly.

The problem: My code seems to work fine, provided I open the 'Host' instance from the Unity Editor, but if I make the full build version the Host it doesnt work.

Strangely all my player-objects will all spawn and act exactly as I intended, but the ball will not spawn unless the 'Host' instance is the one opened inside Unity Editor. I've made the Ball a Network Identity, NetworkTransform etc and Registered Prefab in the NetworkManager in inspector.

Here's the code I am using to spawn the ball on the server, what could be the problem as I really have no ideas, thanks:

Code (CSharp):

1. using UnityEngine;
2. using UnityEngine.Networking;
3.  
4. public class MatchdayManager : NetworkBehaviour {
5. GameObject ballPrefab;  
6.  
7. private void Awake()
8. {
9.     DontDestroyOnLoad(this);
10.  
11.     ballPrefab = Resources.Load<GameObject>("Prefabs/Ball");
12. }
13.  
14. public override void OnStartServer()
15. {
16.     Debug.Log("on server start called");
17.     GameObject go = Instantiate(ballPrefab);
18.     NetworkServer.Spawn(go);
19. }
20.  
21.  
22. }