Unity Crashes On FirstPersonController.GetComponent!!!

When I Use .GetComponent("ScriptName").enabled = true; For The Objects With Blue Font In The Hierarchy, Unity Crashes (Quits). Please Help!!!

here is the script:

 var buttonType : String = "Button Type";
 var mainCharacter : GameObject;
 var character3D : GameObject;
 var car : GameObject;
 var mainCamera : GameObject;
 var gui1 : GameObject;
 var gui2 : GameObject;
 var guix : GameObject;
 function OnMouseDown ()
 {
     if(buttonType == "Drive")
     {
         mainCharacter.GetComponent("Third Person Controller").enabled = false;
         mainCharacter.GetComponent("Third Person Camera").enabled = false;
         mainCharacter.GetComponent("Character Controller").enabled = false; //Disables Main Character And It's Camera Follow
         character3D.GetComponent("Skinned Mesh Renderer").enabled = false; //Hides Main Character
         car.GetComponent("Car").enabled = true; //Activates Car Script
         mainCamera.GetComponent("Car Camera").enabled = true; //Activates Car Camera
         gui1.GetComponent("GUITexture").enabled = false;
         gui2.GetComponent("GUITexture").enabled = false;
         guix.GetComponent("GUITexture").enabled = false; //Disables GUI's
     }
 }

mainCharacter is 3rd Person Controller character3d is a 3d model inside 3rd person controller (bip pelvis) car is a car from CarTutorial Unity crashes on 3rd person controller.