NullReferenceException:Object reference not set to an instance of an object

I create a menu of game script: var quit=false;

function OnMouseEnter() {

   GetComponent.renderer.material.color = Color.red;                        //Change Color to red!        
 

}

function OnMouseExit() {

  GetComponent.renderer.material.color = Color.white;                     //Change Color to white!
 

}

function OnMouseUp() {

     if (quit == true)
   {
       Application.Quit();                                    //If you click on quit aplication quits.
   }
   else
   {
       Application.LoadLevel(1);                              //If you click on other button if loads game!
   }
 

}

function Update() { if (Input.GetKey(KeyCode.Escape)) //If you press (escape) game force closes! { Application.Quit(); } }

and when I get into game mode error occurs: NullReferenceException: Object reference not set to instance of year year object.Please help