Ios admob Interstitual presentFromRootViewController不显示ad

我有一个基于选项卡视图的iOS应用程序，我想使用AdMob Gadial

        if (gadFullReady) { //this check if GAD interstitial received ad
            NSLog(@"from GAD");
            [gadFull presentFromRootViewController:self];
        }

没有显示AdMob Interstitual，我收到如下错误消息：

        Warning: Attempt to present <GADWebAppViewController: 0x9965bd0> on <UITabBarController: 0xb24ab00> while a presentation is in progress!

这一次我收到了错误信息：

       above view <UINavigationController: 0x99cbbe0>
       Warning: Attempt to dismiss from view controller <UITabBarController: 0x9992890> while a presentation or dismiss is in progress!

上图
警告：当演示或取消正在进行时，尝试从视图控制器取消！

有人知道为什么吗？蒂亚

- (void)viewDidLoad
{
    [super viewDidLoad];
    _iSel=0;
    self.tableView.separatorStyle = UITableViewCellSeparatorStyleNone;
    if ([[[UIDevice currentDevice] systemVersion] floatValue] >= 7.0f) self.tableView.tintColor = kIHLightColor;
    [self.tableView setContentOffset:CGPointMake(0, -20)];
    [self.tableView setContentInset:UIEdgeInsetsMake(20, 0, 0, 0)];

    self.tableView.backgroundColor = kIHMenuCellBackgroundColor;
}

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
    [self.tableView selectRowAtIndexPath:[NSIndexPath indexPathForRow:_iSel inSection:0]
                                animated:NO
                          scrollPosition:UITableViewScrollPositionNone];
}

保存选择值

- (void)viewDidLoad
{
    [super viewDidLoad];
    _iSel=0;
    self.tableView.separatorStyle = UITableViewCellSeparatorStyleNone;
    if ([[[UIDevice currentDevice] systemVersion] floatValue] >= 7.0f) self.tableView.tintColor = kIHLightColor;
    [self.tableView setContentOffset:CGPointMake(0, -20)];
    [self.tableView setContentInset:UIEdgeInsetsMake(20, 0, 0, 0)];

    self.tableView.backgroundColor = kIHMenuCellBackgroundColor;
}

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
    [self.tableView selectRowAtIndexPath:[NSIndexPath indexPathForRow:_iSel inSection:0]
                                animated:NO
                          scrollPosition:UITableViewScrollPositionNone];
}