Simple Enemy AI not working : NullReferenceException: Object reference not set to an instance of an object

so im trying to get some simple enemy AI down and when i get within the look distance of my enemy it goes yellow as expected, but then i get the error:

NullReferenceException: Object reference not set to an instance of an object
EnemyAI.lookAt () (at Assets/scripts/EnemyAI.js:33)
EnemyAI.Update () (at Assets/scripts/EnemyAI.js:16)

after that the turn red within a curtain distance and follow function stops working.

here is the script:

var Distance;
var Target : Transform;
var LookAtDistance = 25.0;
var AttackRange = 15.0;
var MoveSpeed = 5.0;
var Damping = 6.0;

function Update ()

{
	Distance = Vector3.Distance(Target.position, transform.position);
	
	if (Distance < LookAtDistance)
	{
		renderer.material.color = Color.yellow;
		lookAt ();
	}
	if (Distance > LookAtDistance)
		
	{
	renderer.material.color = Color.green;
	}
	if (Distance < AttackRange)
	{
	renderer.material.color = Color.red;
	attack ();
	}
}

function lookAt ()
{
	var Rotation = Quaternion.LookRotation(Target.position - transform.position);
	transform.Rotation = Quaternion.Slerp(transform.Rotation, Rotation, Time.deltaTime * Damping);
}

function attack ()
{
	transform.Translate(Vector3.forward * MoveSpeed * Time.deltaTime);
}

can anyone help?

P.S im a noob so please explain in simple terms please ^^

Try:

transform.rotation = Quaternion.Slerp(transform.rotation, Rotation, Time.deltaTime * Damping);

not:

transform.Rotation = Quaternion.Slerp(transform.Rotation, Rotation, Time.deltaTime * Damping);

figured out the problem myself, i had attached the wrong character controller