Roll a Ball Tutorial problem

I used the code given to me in the site, I'm using Unity 5.4.3 with this project and every time I check the code it says MonoBehaviour has unknown format!: Base Type: MonoBehaviour ByteSize:-1 MetaFlag;32768 (node index; o)

This is the code I;m using using UnityEngine; using System.Collections;

 public class PlayerController : MonoBehaviour {
 
     public float speed;
 
     private Rigidbody rb;
 
     void Start ()
     {
         rb = GetComponent<Rigidbody>();
     }
 
     void FixedUpdate ()
     {
         float moveHorizontal = Input.GetAxis ("Horizontal");
         float moveVertical = Input.GetAxis ("Vertical");
 
         Vector3 movement = new Vector3 (moveHorizontal, 0.0f, moveVertical);
 
         rb.AddForce (movement * speed);
     }
 }

I use the error checker in Visual Studio but it says there are 0 errors, 0 warnings, 0 messages.