You can use admob as an alternative when pubcenter ads failed. Add a error_occured event handler and place the following code for this event handler. You won't need a adrotator then!
private void AdControl_ErrorOccurred(object sender, Microsoft.Advertising.AdErrorEventArgs e)
{
AdControl ad = (AdControl)sender;
Grid grd = (Grid)ad.Parent;
System.Windows.Deployment.Current.Dispatcher.BeginInvoke(() =>
{
AdView bannerAd = new AdView
{
Format = AdFormats.Banner,
AdUnitID = AppSettings.ADMOBAPPID
};
AdRequest adRequest = new AdRequest();
grd.Children.Add(bannerAd);
bannerAd.LoadAd(adRequest);
});
System.Diagnostics.Debug.WriteLine(e.Error.Message);
}
This is explained more comprehensively here http://www.windowsapptutorials.com/windows-phone/advertising/adding-microsoft-pubcenter-ads-in-windows-phone-8-apps/