health bar error "Null Referenc Exception"

hey i want to creat a health bar i follow this guy http://www.youtube.com/watch?v=vNJbFtd6gBc but unity give a error "Null Referenc Exception"

static var healthcount:int=100;

var health00:Texture2D;

var health10:Texture2D; var health20:Texture2D;

var health30:Texture2D; var health40:Texture2D; var health50:Texture2D; var health60:Texture2D; var health70:Texture2D; var health80:Texture2D; var health90:Texture2D; var health100:Texture2D;

function Start () {

}

function Update () { var healthtexture = gameObject.Find("health 100"); Healthcount=20; if(Healthcount < 30){ Debug.Log("hello"); healthtexture.guiTexture.texture = health20;

 }

}