Windows Phone 8 -插页式广告只显示一次

我设法让adMob插播式广告在我的手机应用中发挥作用。然而，他们只提供一个广告，然后没有更多的广告。这就好像我需要"重置"地址或其他东西，但我找不到更多的信息，除了adMob的例子，不重复提供广告。

在下面的代码中发生的事情是，一旦'count'在按钮中点击5，我想要一个add来显示。

任何想法?非常感谢。

public partial class MainPage : PhoneApplicationPage
{
    /* Intersitial*/
    private InterstitialAd interstitialAd;
    int countAds = 0;
    AdRequest adRequest = new AdRequest();
    // Constructor
    public MainPage()
    {
        InitializeComponent();
        /* Intersitial */
        interstitialAd = new InterstitialAd("MY_ID");
        adRequest = new AdRequest();
    }
    private void Button_Click(object sender, RoutedEventArgs e)
    {
        countAds++;
        if (countAds >= 5)
        {
            interstitialAd.ReceivedAd += OnAdReceived;
            interstitialAd.LoadAd(adRequest);
            countAds = 0;
        }
    }
     /* Intersital */
    private void OnAdReceived(object sender, AdEventArgs e)
    {
        System.Diagnostics.Debug.WriteLine("Ad received successfully");
        interstitialAd.ShowAd();
    }

public partial class MainPage : PhoneApplicationPage
{
    private InterstitialAd interstitialAd;
    int Click1 = 0;
    AdRequest adRequest = new AdRequest();
    public MainPage()
    {
        InitializeComponent();          
     }
    private void Button_Click(object sender, RoutedEventArgs e)
    {
        Click1++;
        if (Click1 == 5)
        {
            interstitialAd = new InterstitialAd("My APp Id");
            AdRequest adRequest = new AdRequest();
              interstitialAd.ReceivedAd += OnAdReceived;
            interstitialAd.LoadAd(adRequest);
            Click1 = 0;
        }
    }
    private void OnAdReceived(object sender, AdEventArgs e)
    {
        System.Diagnostics.Debug.WriteLine("Ad received successfully");
        interstitialAd.ShowAd();   
    }
}