I’m following the tutorial on RevMob for implementing banner ads in my mobile game, and I keep getting an error that says "NullReferenceException: Object reference not set to an instance of an object RevMobID.Start ()".  I'm still a novice programmer, so this could be a simple issue.  Here’s what I have:

public class RevMobID : MonoBehaviour 
{

private RevMobBanner banner;

private static readonly Dictionary<String, String> REVMOB_APP_IDS = new Dictionary<String, String> ()
 {
      {"IOS", "(my ad ID here)"}
 };
 private RevMob revmob;

 void Awake()
 {
      Debug.Log ("RevMob start);
      revmob = RevMob.Start (REVMOB_APP_IDS, "Banner Ad");
 }

 void Start()
 {
      #if UNITY_IPHONE
           banner = revmob.CreateBanner(0, 0, Screen.width, Screen.height/10, null, null); // the console pinpoints the error here
           banner.Show();
      #endif
 }