Hi, I had a null reference error on not being able to find the ScoreKeeper object. This was easily solved but Gary has obviously added the ScoreKeeper prefab to the GameOver scene without recording that step. When ScoreKeeper becomes a singleton this error should also disappear when starting the game from the Main Menu.
So to all of those people who are getting the null reference error just add the prefab ScoreKeeper to the project hierarchy.
