Rotate an sphere by mouse inputs

Hi there, I've tried script after script to get this to work!

its simple... I want a sphere to rotate in the direction that the mouse is, nothing fancy just simply rotate around its centre point and the top face the mouse position at all times.

tried this script, but its just refuses to work

// LookAtMouse will cause an object to rotate toward the cursor, along the y axis.
// To use, drop on an object that should always look toward the mouse cursor.
// Change the speed value to alter how quickly the object rotates toward the mouse.

// speed is the rate at which the object will rotate
var speed = 4.0;

function Update () {
    // Generate a plane that intersects the transform's position with an upwards normal.
    var playerPlane = new Plane(Vector3.up, transform.position);

    // Generate a ray from the cursor position
    var ray = Camera.main.ScreenPointToRay (Input.mousePosition);

    // Determine the point where the cursor ray intersects the plane.
    // This will be the point that the object must look towards to be looking at the mouse.
    // Raycasting to a Plane object only gives us a distance, so we'll have to take the distance,
    //   then find the point along that ray that meets that distance.  This will be the point
    //   to look at.
    var hitdist = 0.0;
    // If the ray is parallel to the plane, Raycast will return false.
    if (playerPlane.Raycast (ray, hitdist)) {
        // Get the point along the ray that hits the calculated distance.
        var targetPoint = ray.GetPoint(hitdist);

        // Determine the target rotation.  This is the rotation if the transform looks at the target point.
        var targetRotation = Quaternion.LookRotation(targetPoint - transform.position);

        // Smoothly rotate towards the target point.
        transform.rotation = Quaternion.Slerp(transform.rotation, targetRotation, speed * Time.deltaTime);

NullReferenceException UnityEngine.Camera.ScreenPointToRay (Vector3 position) towardscamera.Update () (at Assets/Scripts/towardscamera.js:14)

If anyone understands that!

thanks - Caius

Looks like you haven't tagged a camera as Main Camera

Camera.main looks in the scene for active GameObjects with the "MainCamera" tag, which have an active Camera component on

Add that tag to your scene camera and it should fix it