Cant disable first person controller C# Unity 5

can anyone see what i am doing wrong?
I am trying to disable the first person controller.
My script has the name space, it has a reference to the object with the firstpersoncontroller script on it.
But i keep getting the error:
NullReferenceException: Object reference not set to an instance of an object
SwitchCameraPosition.Update () (at Assets/Main Menu/SwitchCameraPosition.cs:48)

The error is strange to me, because the reference to the cubeCameraSwitch "is used" correct in the code's transform section.

Hope u can help

Code (CSharp):

1. using UnityEngine;
2. using System.Collections;
3. using UnityStandardAssets.Characters.FirstPerson;
4.  
5. public class SwitchCameraPosition: MonoBehaviour
6. {
7.     private bool switchViewA;
8.     private bool switchViewB;
9.     public float XPosOld;
10.     public float YPosOld;
11.     public float ZPosOld;
12.     public float XPosNew;
13.     public float YPosNew;
14.     public float ZPosNew;
15.     public Transform target;  
16.     public float smoothing = 10000f;        
17.     Vector3 offset;                    
18.  
19.     private GameObject cubeCameraSwitch;
20.     private GameObject player;
21.  
22.     void Start ()
23.     {
24.  
25.         switchViewB = true;
26.         switchViewA = false;
27.         cubeCameraSwitch = GameObject.FindGameObjectWithTag("CubeCameraSwitch");
28.         player = GameObject.FindGameObjectWithTag("Player");
29.    
30.         offset = transform.position - target.position;
31.  
32.     }
33.    
34.    
35.     void Update ()
36.     {
37.  
38.        
39.         if (Input.GetButton ("SwitchView"))
40.         {
41.             switchViewB = false;
42.             switchViewA = true;
43.             cubeCameraSwitch.GetComponent<FirstPersonController>().enabled = false;
44.            
45.         }
46.  
47.         if (switchViewA == true)
48.         {
49.             cubeCameraSwitch.transform.localPosition = new Vector3 (XPosNew ,player.transform.position.y + YPosNew,+ ZPosNew);
50.             transform.localEulerAngles = new Vector3 (0,0,0);
51.             Debug.Log ("Switched To First Person View");
52.             offset = transform.position;
53.             switchViewA = false;
54.  
55.    
56.         }
57.        
58.         if (Input.GetButton ("Fire1"))
59.         {
60.             switchViewA = false;
61.             switchViewB = true;
62.             cubeCameraSwitch.GetComponent<FirstPersonController>().enabled = true;
63.         }
64.  
65.         if (switchViewB == true)
66.         {
67.             cubeCameraSwitch.transform.localPosition = new Vector3 (XPosOld ,player.transform.position.y + YPosOld ,ZPosOld);
68.             transform.localEulerAngles = new Vector3 (30,0,0);
69.             Debug.Log ("Switched To God View");
70.             offset = transform.position;
71.             switchViewB = false;
72.  
73.         }
74.         if (switchViewA == false && switchViewB == false)
75.         {
76.             // Calculate the initial offset.
77.             //offset = transform.position - target.position;
78.             // Create a postion the camera is aiming for based on the offset from the target.
79.             Vector3 targetCamPos = target.position + offset;
80.        
81.             // Smoothly interpolate between the camera's current position and it's target position.
82.             transform.position = Vector3.Lerp (transform.position, targetCamPos, smoothing * Time.deltaTime);
83.         }
84.     }
85.  
86.    
87.  
88.  
89. }
90.