Joystick problems

Hey I am building a 2D game at the moment, with a joystick to move the character around. I Used this Joystick the same on a 3D game that worked fine. However when I am using it on my 2D i get an error saying: NullReferenceException: Object reference not set to an instance of an object

Under the movement line of code in my PlayerController script:

 public Rigidbody2D rb;
 public float speed;
 public Animator anim;

 private ManagerJoystick _mngrJoystick;
 private float inputX;
 private float inputZ;
 private Vector2 m_Movement;

 void start()
 {
     rb = GetComponent<Rigidbody2D>();
     _mngrJoystick = GameObject.Find("Joystick").GetComponent<ManagerJoystick>();
 }

 void Movement()
 {
     inputX = _mngrJoystick.inputHorizontal();
     inputZ = _mngrJoystick.inputVertical();
 }

 void FixedUpdate()
 {
     Movement();

 }

}

This is how the JoyStickManager has been setup at the bottom in the public float Vertical & Horizontal input:

 void Start()
 {
     imgJoystickBg = GetComponent<Image>();
     imgJoystick = transform.GetChild(0).GetComponent<Image>();
 }

 public void OnDrag(PointerEventData eventData)
 {
     if (RectTransformUtility.ScreenPointToLocalPointInRectangle(
         imgJoystickBg.rectTransform,
         eventData.position,
         eventData.pressEventCamera,
         out posInput))
     {
         posInput.x = posInput.x / (imgJoystickBg.rectTransform.sizeDelta.x);
         posInput.y = posInput.y / (imgJoystickBg.rectTransform.sizeDelta.y);

         if (posInput.magnitude > 1f)
         {
             posInput = posInput.normalized;
         }

         imgJoystick.rectTransform.anchoredPosition = new Vector2(
             posInput.x * (imgJoystickBg.rectTransform.sizeDelta.x / 2),
             posInput.y * (imgJoystickBg.rectTransform.sizeDelta.y / 2));
     }
 }

 public void OnPointerDown(PointerEventData eventData)
 {
     OnDrag(eventData);
 }

 public void OnPointerUp(PointerEventData eventData)
 {
     posInput = Vector2.zero;
     imgJoystick.rectTransform.anchoredPosition = Vector2.zero;
 }

 public float inputHorizontal()
 {
     if (posInput.x != 0)
         return posInput.x;
     else
         return Input.GetAxis("Horizontal");
 }

 public float inputVertical()
 {
     if (posInput.y != 0)
         return posInput.y;
     else
         return Input.GetAxis("Vertical");
 }

}