Scripting troubles.

I'm trying to get a 2d character to move in a simple platformer, so i copied over the 2d assets package that unity offers and changed the names of some things to fit my assets but i keep getting this problem,
"NullReferenceException: Object reference not set to an instance of an object
UnityStandardAssets._2D.moveWorking.FixedUpdate () (at Assets/script/moveWorking.cs:39)"

I'm not quite sure what it means by an instance of an object.
here is my code.

Code (CSharp):

1. using System;
2. using UnityEngine;
3. namespace UnityStandardAssets._2D
4. {
5.     public class moveWorking : MonoBehaviour
6.     {
7.         [SerializeField] private float m_MaxSpeed = 10f;                    // The fastest the player can travel in the x axis.
8.         [SerializeField] private float m_JumpForce = 400f;                  // Amount of force added when the player jumps.
9.         [Range(0, 1)] [SerializeField] private float m_CrouchSpeed = .36f;  // Amount of maxSpeed applied to crouching movement. 1 = 100%
10.         [SerializeField] private bool m_AirControl = false;                 // Whether or not a player can steer while jumping;
11.         [SerializeField] private LayerMask m_WhatIsGround;                  // A mask determining what is ground to the character
12.      
13.         private Transform m_GroundCheck;    // A position marking where to check if the player is grounded.
14.         const float k_GroundedRadius = .2f; // Radius of the overlap circle to determine if grounded
15.         private bool m_Grounded;            // Whether or not the player is grounded.
16. //        private Transform m_CeilingCheck;   // A position marking where to check for ceilings
17.         const float k_CeilingRadius = .01f; // Radius of the overlap circle to determine if the player can stand up
18.         private Animator m_Anim;            // Reference to the player's animator component.
19.         private Rigidbody2D m_Rigidbody2D;
20.         private bool m_FacingRight = true;  // For determining which way the player is currently facing.
21.      
22.         private void Awake()
23.         {
24.             // Setting up references.
25.             m_GroundCheck = transform.Find("GroundCheck");
26. //            m_CeilingCheck = transform.Find("CeilingCheck");
27.             m_Anim = GetComponent<Animator>();
28.             m_Rigidbody2D = GetComponent<Rigidbody2D>();
29.         }
30.      
31.      
32.         private void FixedUpdate()
33.         {
34.             m_Grounded = false;
35.          
36.             // The player is grounded if a circlecast to the groundcheck position hits anything designated as ground
37.             // This can be done using layers instead but Sample Assets will not overwrite your project settings.
38.             Collider2D[] theDon = Physics2D.OverlapCircleAll(m_GroundCheck.position, k_GroundedRadius, m_WhatIsGround);
39.             for (int i = 0; i < theDon.Length; i++)
40.             {
41.                 if (theDon[i].gameObject != gameObject)
42.                     m_Grounded = true;
43.             }
44.             m_Anim.SetBool("Ground", m_Grounded);
45.          
46.             // Set the vertical animation
47.             m_Anim.SetFloat("vSpeed", m_Rigidbody2D.velocity.y);
48.         }
49.      
50.      
51.         public void Move(float move, bool crouch, bool jump)
52.         {
53.             // If crouching, check to see if the character can stand up
54.         //    if (!crouch && m_Anim.GetBool("Crouch"))
55.             {
56.                 // If the character has a ceiling preventing them from standing up, keep them crouching
57.             //    if (Physics2D.OverlapCircle(m_CeilingCheck.position, k_CeilingRadius, m_WhatIsGround))
58.                 {
59.             //        crouch = true;
60.                 }
61.             }
62.          
63.             // Set whether or not the character is crouching in the animator
64. //            m_Anim.SetBool("Crouch", crouch);
65.          
66.             //only control the player if grounded or airControl is turned on
67.             if (m_Grounded || m_AirControl)
68.             {
69.                 // Reduce the speed if crouching by the crouchSpeed multiplier
70.                 move = (crouch ? move*m_CrouchSpeed : move);
71.              
72.                 // The Speed animator parameter is set to the absolute value of the horizontal input.
73.                 m_Anim.SetFloat("Speed", Mathf.Abs(move));
74.              
75.                 // Move the character
76.                 m_Rigidbody2D.velocity = new Vector2(move*m_MaxSpeed, m_Rigidbody2D.velocity.y);
77.              
78.                 // If the input is moving the player right and the player is facing left...
79.                 if (move > 0 && !m_FacingRight)
80.                 {
81.                     // ... flip the player.
82.                     Flip();
83.                 }
84.                 // Otherwise if the input is moving the player left and the player is facing right...
85.                 else if (move < 0 && m_FacingRight)
86.                 {
87.                     // ... flip the player.
88.                     Flip();
89.                 }
90.             }
91.             // If the player should jump...
92.             if (m_Grounded && jump && m_Anim.GetBool("Ground"))
93.             {
94.                 // Add a vertical force to the player.
95.                 m_Grounded = true;
96.                 m_Anim.SetBool("Ground", false);
97.                 m_Rigidbody2D.AddForce(new Vector2(0f, m_JumpForce));
98.             }
99.         }
100.      
101.      
102.         private void Flip()
103.         {
104.             // Switch the way the player is labelled as facing.
105.             m_FacingRight = !m_FacingRight;
106.          
107.             // Multiply the player's x local scale by -1.
108.             Vector3 theScale = transform.localScale;
109.             theScale.x *= -1;
110.             transform.localScale = theScale;
111.         }
112.     }
113. }

 

it means this line didn't find any colliders in the radius. did you set "m_WhatIsGround" properly?

 

from another website i figured out that WhatIsGround is the layer, so i switched that with the layer that the objects he is running on, it is still coming up with the same error, but he is now able to move.