Prefab Initiated At Beginning Of Game Returns Error When Script On Prefab Attempts To Find A Gameobject In Game

I Have 20 Prefabs Being Initiated At The Beginning Of The Game. The Prefab Has A Script Called "Biker.cs", The Script Has 5 Private Gameobjects:

 private GameObject pauseMenu;
 private GameObject settingsMenu;
 private GameObject videoMenu;
 private GameObject audioMenu;
 private GameObject quitMenu;

In "void Start () { }" I Initiate Each Gameobject With:

 pauseMenu = GameObject.Find("PauseMenu");
 settingsMenu = GameObject.Find("SettingsMenu");
 videoMenu = GameObject.Find("VideoMenu");
 audioMenu = GameObject.Find("AudioMenu");
 quitMenu = GameObject.Find("QuitMenu");

I Then Use Each Gameobject In "void OnGUI () { }" Like So:

 if (hovering == true && pauseMenu.activeInHierarchy == false && settingsMenu.activeInHierarchy == false && videoMenu.activeInHierarchy == false && audioMenu.activeInHierarchy == false && quitMenu.activeInHierarchy == false)
         {
 
             //If not paused display gui, if paused do nothing
             if (pauseCounter == 1)
             {
 
                 Vector2 mousePos = new Vector2(Event.current.mousePosition.x, Event.current.mousePosition.y);
 
                 //Creates a text box displaying "clickedBikeFitness"
                 GUI.Box(new Rect((mousePos.x + 20f), mousePos.y, 80, 20), "" + networkFitness);
 
             }
 
         }

At The Beginning Of The Game It Gives Me An Error In The Console Saying

"NullReferenceException: Object reference not set to an instance of an object Biker.OnGUI () (at Assets/Scripts/NeuralNetwork/Biker.cs:167)"

I Have Used This Exact Method In Other Scripts To Check Whether Or Not These Gameobjects Are Active.

I Have Also Double Checked And Made Sure Each Gameobjects Name Is The Exact Same Name In-Game.

Question: Why Does It Give Me This Error On This Script And Not On Others Which I Did The Same Thing For?

Notes:

I Have Used This Exact Method In Other Scripts To Check Whether Or Not These Gameobjects Are Active.

I Have Also Double Checked And Made Sure Each Gameobjects Name Is The Exact Same Name In-Game.

Each Gameobject Is Parented Under A "Canvas" Gameobject, But In The Other Scripts I Have Used This Method I Just Had To Specify The Name And Not The Path.

I Am Using Unity 2017.1.0f3 Personal Version

I Am Using Microsoft Visual Studios Community 2017 Version 15.3.2