simple MasterDetailPage throws exception

I have a very simple Code, works great with Android, but when I try to debugg ist on Win8Phone I get following error(in the App.xaml.cs where the debugger stops):

// Code to execute if a navigation fails
        private void RootFrame_NavigationFailed(object sender, NavigationFailedEventArgs e)
        {
            if (Debugger.IsAttached)
            {
                // A navigation has failed; break into the debugger
                Debugger.Break();
            }
        }

Here is my simple Sample Code: Btw. I use Xamarin Forms 1.2.3.6257

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Xamarin.Forms;

namespace App10
{
    public class App
    {
        public static MasterDetailPage MeisterT = new MasterDetailPage
        {
            Master = new ContentPage
            {
                Content = new Label
                {
                    Text = "Hallo"
                    Font = Font.BoldSystemFontOfSize(30)
                }
            }

            Detail = new ContentPage
            {
                Content = new Label
                {
                    Text = "Hallo Detail"
                    Font = Font.BoldSystemFontOfSize(30)
                }
            }
        };

        public static Page GetMainPage()
        {
            return MeisterT;
        }
    }
}