适用于Xamarin的Facebook iOS SDK提供了一条奇怪的错误消息

Question

我正在尝试学习如何使用Facebook iOS SDK for Xamarin。试图制作一个非常简单的应用程序，只需登录，然后在标签中显示您的名字。但是我收到此错误消息，我在互联网上找不到任何有关的信息。当我尝试使用SDK附带的一些示例应用程序时，我也收到此错误消息。错误消息如下：

这是我在ViewController中添加的内容，其他所有内容都未触及标准项目：

    private string [] ExtendedPermissions = new [] { "user_about_me", "public_profile", "read_stream"};
    FBLoginView loginView;
    IFBGraphPerson user;

    public override void ViewDidLoad ()
    {
        base.ViewDidLoad ();
        loginView = new FBLoginView (ExtendedPermissions) {
            Frame = new RectangleF(85, 20, 151, 43)
        };

        loginView.FetchedUserInfo += (sender, e) => {
            user = e.User;
            LoginLabel.Text = user.GetName();
        };

        View.AddSubview (loginView);
    }

这是在AppDelegate中：

        public override bool FinishedLaunching (UIApplication app, NSDictionary options)
    {
        FBSettings.DefaultAppID = FacebookAppId;
        FBSettings.DefaultDisplayName = DisplayName;
        return true;
    }

    public override bool OpenUrl (UIApplication application, NSUrl url, string sourceApplication, NSObject annotation)
    {
        // We need to handle URLs by passing them to FBSession in order for SSO authentication
        // to work.
        return FBSession.ActiveSession.HandleOpenURL(url);
    }

    public override void OnActivated (UIApplication application)
    {
        // We need to properly handle activation of the application with regards to SSO
        // (e.g., returning from iOS 6.0 authorization dialog or from fast app switching).
        FBSession.ActiveSession.HandleDidBecomeActive();
    }

如果有人知道这个错误意味着什么，我将非常感激！