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

i keep getting the error nullreferenceexception and it also will not display the GUIs even though i have set the variables and the lifePercent variable seems to be functioning correctly. Any help on fixing the error and showing GUIs? (script worked perfect untill i added the section to draw the GUIs)

Health and GUI code-

 var MaxHealth = 100;
 var Health : int;
 
 function Start ()
 {
     Health = MaxHealth;
     onGUI();
 }
 
 function ApplyDamage (TheDamage : int)
 {
     Health -= TheDamage;
     
     if(Health <= 0)
     {
         Dead();
     }
 }
 
 function Dead()
 {
     RespawnMenuV2.playerIsDead = true;
     Debug.Log("Player Died");
 }
 
 function RespawnStats ()
 {
     Health = MaxHealth;
 }
 
 var lifeRemainingBehindTexture : Texture;
 var lifeRemainingTexture : Texture;
 var lifePercent : float;
 
 private var left : float;
 private var top : float;
 private var backgroundWidthLife : float;
 private var lifeWidth : float;
 private var height : float;
 
 function onGUI()
 {
     lifePercent = Health / MaxHealth;
     
     left = Screen.width / 2;
     top = 8;
     backgroundWidthLife = Screen.width / 4;
     lifeWidth = lifePercent * backgroundWidthLife;
     height = 12;
     
     //players health GUI drawing
     GUI.DrawTexture(Rect(left,top,backgroundWidthLife,height), lifeRemainingBehindTexture, ScaleMode.StretchToFill, true, 1.0);
     GUI.DrawTexture(Rect(left,top,lifeWidth,height), lifeRemainingTexture, ScaleMode.StretchToFill, true, 1.0);
 }