爲什麼不能運行WpfBrowserApplication？

我做了一個應該顯示小的MessageBox的小程序。爲什麼不能運行WpfBrowserApplication？

using System; 
using System.Collections.Generic; 
using System.Linq;  
using System.Text;  
using System.Windows;  
using System.Windows.Controls;  
using System.Windows.Data;  
using System.Windows.Documents;  
using System.Windows.Input;  
using System.Windows.Media; 
using System.Windows.Media.Imaging; 
using System.Windows.Navigation; 
using System.Windows.Shapes; 

namespace WpfBrowserApplication1 
{ 
    /// <summary>  
    /// Interaction logic for Page1.xaml 
    /// </summary>  
    public partial class Page1 : Page  
    { 
     public Page1()  
     {  
      InitializeComponent();  
     } 

     private void button1_Click(object sender, RoutedEventArgs e)  
     { 

      MessageBox.Show("gs");  
     } 
    }  
}

結果：

enter image description here