I don't know what to do with the object reference error.

This may be me being ignorant of detail but i think I have either made a mistake or am missing a key part in this code. I’ve input the following lines of code from the roll-a-ball tutorial and it comes up with error CS0120 and asks for object reference. Please tell me if I have made a mistake. The error displays over the last full line of code.

using UnityEngine;

using System.Collections;

public class PlayerController : MonoBehaviour
public float speed;

void FixedUpdate ()
	float moveHorizontal = Input.GetAxis("Horizontal");
	float moveVertical = Input.GetAxis("Vertical");

	Vector3 movement = new Vector3(moveHorizontal, 0.0F, moveVertical);

	Rigidbody.AddForce(movement * speed * Time.deltaTime);


Rigidbody is a class. rigidbody is a shortcut to GetComponent(), which accesses the instance of the class on this object. So, try:

rigidbody.AddForce(movement * speed * Time.deltaTime);