Change hieght on smooth follow OnTriggerEnter

I am trying to make my script tell the smooth follow script to change the height to 0.5 when I enter the trigger. But I keep getting this error when I hit the trigger "NullReferenceException: Object reference not set to an instance of an object Boo.Lang.Runtime.RuntimeServices.GetDispatcher (System.Object target, System.String cacheKeyName, System.Type[] cacheKeyTypes, Boo.Lang.Runtime.DynamicDispatching.DispatcherFactory factory) Boo.Lang.Runtime.RuntimeServices.GetDispatcher (System.Object target, System.Object[] args, System.String cacheKeyName, Boo.Lang.Runtime.DynamicDispatching.DispatcherFactory factory) Boo.Lang.Runtime.RuntimeServices.SetProperty (System.Object target, System.String name, System.Object value) Camera Down.OnTriggerEnter (UnityEngine.Collider hitPlayer) (at Assets/Camera Down.js:8)"

My Script

private var MainCamera : GameObject; MainCamera = GameObject.FindWithTag ("MainCamera");

function OnTriggerEnter (hitPlayer : Collider) { if(hitPlayer.gameObject.tag == "Army Cube") {

 MainCamera.GetComponent("Smooth Follow").height = 0.5;
 

}

}