Hi
It was working, then this error just came out of nowhere. Don’t understand whats going on.
Its a top down shooter and the idea being that it aims and shoots using the curser.
Can anyone offer any suggestions please. Really am stuck with this one. 
public class PlayerController : MonoBehaviour
{
//handling
public float rotationSpeed = 1000;
public float speed = 20;
public float fireRate;
private float nextFire;
//system
private Quaternion targetRotation; //stores direction
public PlayerBoundary boundary;
//components
private CharacterController controller;
private Camera cam;
public GameObject shot;
public Transform shotSpawn;
void Start()
{
controller = GetComponent<CharacterController> ();
cam = Camera.main;
}
void Update()
{
ControlMouse ();
if (Input.GetButton ("Shoot") && Time.time > nextFire)
{
nextFire = Time.time + fireRate;
Instantiate(shot, shotSpawn.position, shotSpawn.rotation);
audio.Play ();
}
}
void ControlMouse()
{
//set up direction in input variabe
Vector3 input = new Vector3(Input.GetAxisRaw("Horizontal"),0, Input.GetAxisRaw("Vertical"));
//Sets up mouse position
Vector3 mousePos = Input.mousePosition;
mousePos = cam.ScreenToWorldPoint (new Vector3 (mousePos.x, mousePos.y, cam.transform.position.y - transform.position.y));
shotSpawn.LookAt(mousePos);
if (input != Vector3.zero) //fingers taken off controls, player doesnt reset to defaul position
{
targetRotation = Quaternion.LookRotation(input); //rotates player in the way of the direction
transform.eulerAngles = Vector3.up * Mathf.MoveTowardsAngle(transform.eulerAngles.y, targetRotation.eulerAngles.y, rotationSpeed * Time.deltaTime);
}
//Controls Movement
Vector3 motion = input;
motion *= (Mathf.Abs (input.x) == 1 && Mathf.Abs (input.z) == 1) ? .7f : 1; //moving diagonally doesnt travel at twice the speed
controller.Move (motion * speed * Time.deltaTime);
}
}