MoPub banner Ad not appearing - objective-c

Question

I'm trying to get a MoPub banner ad to appear. I've created a UIViewController, and put the MoPub code into the View did load as thus..
- (id)init
{
self = [super init];
if (self) {
// Custom initialization
}
return self;
}
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view.
// ... your other -viewDidLoad code ...
self.adView = [[MPAdView alloc] initWithAdUnitId:#"ID HERE"
size:MOPUB_BANNER_SIZE];
self.adView.delegate = self;
CGRect frame = self.adView.frame;
CGSize size = [self.adView adContentViewSize];
frame.origin.y = [[UIScreen mainScreen] applicationFrame].size.height - size.height;
self.adView.frame = frame;
[self.view addSubview:self.adView];
[self.adView loadAd];
//[super viewDidLoad];
}
#pragma mark - <MPAdViewDelegate>
- (UIViewController *)viewControllerForPresentingModalView {
return self;
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
And in my AppDelegate I'm setting everything up like this (it's a Sparrow game)
//setup Sparrow
CGRect screenBounds = [UIScreen mainScreen].bounds;
_window = [[UIWindow alloc] initWithFrame:screenBounds];
_gcViewController = [[UIViewController alloc]init];
_viewController = [[SPViewController alloc] init];
[_viewController startWithRoot:[Game class] supportHighResolutions:YES doubleOnPad:YES];
_viewController.multitouchEnabled = YES;
[_window setRootViewController:_viewController];
adViewController = [[AdViewController alloc]init];
[_window addSubview:adViewController.view];
[_window addSubview:_gcViewController.view];
[_window makeKeyAndVisible];
And in the console I seem to be getting the correct msgs as this...
Looking for custom event class named MPHTMLBannerCustomEvent. MOPUB:
Loading MoPub HTML banner MOPUB: MoPub HTML banner did load
But I can't see anything on the screen in the simulator, any ideas?