NullReferenceException error

function Update() {

var kEy = GameObject.Find("Key"); var Sec_KEY = GameObject.Find("Second Key"); var Pc = GameObject.Find("PC"); var Npc = GameObject.Find("NPC"); var invis_Wall = GameObject.Find("Mesh Collider");

var NpcDist = Vector3.Distance(Pc.transform.position, Npc.transform.position); var kEyDist = Vector3.Distance(Pc.transform.position, kEy.transform.position); var SecondDist = Vector3.Distance(Pc.transform.position, Sec_KEY.transform.position); var kEyDist1 = Vector3.Distance(kEy.transform.position, Npc.transform.position);

     if(NpcDist < 2){
         if(!kEy.transform.IsChildOf(Pc.transform)){
             dialon = 1;
             screenText = "Break me out of here and I might help you to find one \n of the Shadow Thieves safehouses. Three keys \n are needed to open these locks. \n The first one is over there in Hunter's Alley. Be \n careful though as the key might be guarded.";
         }
     }
     else {
         dialon = 0;
     }

     if(kEyDist < 2){
         isTrue = 1;
         screenText = "First Key - Take to prisoner";
     }
     else {
         isTrue = 0;
     }

     if(SecondDist < 2){
         isNear = 1;
         screenText = "Second Key - Take to prisoner";
     }
     else{
         isNear = 0;
     }
     if(kEyDist1 < 2){

         screenText = "HOORAY the first key. Now to find that second \n key it's somewhere hidden \n on Jembril Street, I think.";
         ShowChat();
         gameObject.Find("Mesh Collider").active = false;
         kEy.active = false;
         //Destroy(kEyDist);
         dialon1 = 0;
         putdown = 0;

     }
     if(Input.GetKeyDown("m")){
         putdown = 1;
         kEy.transform.parent = Pc.transform;
         kEy.transform.localPosition = Vector3.forward * 1.5;
     }
     else {
         if(Input.GetKeyDown("n")){
             putdown = 0;
             kEy.transform.parent = null;
         }
     }
     if(Input.GetKeyDown("j")){
         putdown1 = 1;
         Sec_KEY.transform.parent = Pc.transform;
         Sec_KEY.transform.localPosition = Vector3.forward * 1.5;
     }
     else {
         if(Input.GetKeyDown("k")){
             putdown1 = 0;
             Sec_KEY.transform.parent = null;
         }
     }
 var fwd = Pc.transform.TransformDirection(Vector3.forward);
 var hit : RaycastHit;
 Debug.DrawRay(Pc.transform.position, fwd * 1, Color.green);
 if(Physics.Raycast(Pc.transform.position, fwd, hit, 1)){

     if(hit.collider.gameObject.name == "Mesh Collider"){

         Debug.Log("Invisiable Wall");
         Debug.Log(hit.distance);

         screenText = "Oh on a invisiable wall, who or \n what placed this thing here. \n Might as well as give the first key \n to the prisoner to get rid of this.";
         ShowWall();

     }
 }

}

function OnGUI () {

 if (dialon>0){

     var dialRect : Rect = Rect ((Screen.width/2)-150, (Screen.height/2)-200, 300, 100);
     GUI.Box(dialRect , screenText);

 }
     if (isTrue>0){

     var dialRect1 : Rect = Rect ((Screen.width/2)-150, (Screen.height/2)-200, 300, 100);
     GUI.Box(dialRect1 , screenText);

 }
     if (isNear>0){

         var dialRect2 : Rect = Rect ((Screen.width/2)-150, (Screen.height/2)-200, 300, 100);
         GUI.Box(dialRect2 , screenText);

 }
     if (wall>0){

         var dialRect100 : Rect = Rect ((Screen.width/2)-150, (Screen.height/2)-200, 300, 100);
         GUI.Box(dialRect100 , screenText);
     }
     if (Key_2_Npc>0) {

         var dialRect3 : Rect = Rect ((Screen.width/2)-150, (Screen.height/2)-200, 300, 100);
         GUI.Box(dialRect3, screenText);
     }

}

function ShowWall() { wall = 1; yield WaitForSeconds(2); wall = 0; }