problems with iAD banner

as it says im having problems putting a simple iAD banner at the bottom of my screen, for some reason i get errors in the code a lot of them even when i use the standard unity doc code, any help please.

HERES THE CODE

 private var banner : ADBannerView = null;
 
     
 
 function ShowBanner() {
 
     while (!banner.loaded && banner.error == null)
 
         yield;
 
         
 
     if (banner.error == null)
 
         banner.Show();
 
     else banner = null;
 
 }
 
  
 
 function OnGUI() {
 
     GUI.enabled = (banner == null ? true : false);
 
     
 
     if (GUILayout.Button("Show Banner")) {
 
         banner = new ADBannerView();
 
         banner.autoSize = true;
 
         banner.autoPosition = ADPosition.Bottom;
 
         StartCoroutine(ShowBanner());
 
     }
 
 }