title: iAds: bannerViewDidLoadAd no longer called after first didFailToReceiveAdWithError
body: <p>I'm testing iAds in XCode 4.</p>
  
  <p>Everything works fine, until the first time a <code>bannerView:didFailToReceiveAdWithError:</code> is received, which I react to by sliding the banner off the screen.</p>
  
  <pre><code>//move the ad back off the screen if an error occurs
  - (void)bannerView:(ADBannerView *)banner didFailToReceiveAdWithError:(NSError *)error {
      if (self.bannerIsInScreenBounds)
      {
          [UIView beginAnimations:@"animateAdBannerOff" context:NULL];
          // move the banner view off the screen.
          banner.frame = CGRectOffset(banner.frame, 320, 0);
          [UIView commitAnimations];
      }
  }
  </code></pre>
  
  <p>After that, no more <code>bannerViewDidLoadAd:</code> messages are sent to the ADBannerViewDelegate. I'm logging that method right at the top, it's not being called any more.</p>
  
  <p>I'm not releasing the banner or anything, and the ADBannerViewDelegate class is still there and doing other stuff.</p>
  
  <p>What could be wrong?</p>
  
  <p>Thanks.</p>