<Application x:Class="NavigationApplication.App" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" StartupUri="StartupWindow.xaml" NavigationFailed="App_NavigationFailed"> </Application> //File:Window.xaml.cs using System; using System.Windows; using System.Data; using System.Xml; using System.Configuration; using System.Windows.Threading; using System.Windows.Navigation; namespace NavigationApplication { public partial class App : System.Windows.Application { private void App_NavigationFailed(object sender, NavigationFailedEventArgs e) { if (e.Exception is System.Net.WebException) { MessageBox.Show("Website " + e.Uri.ToString() + " cannot be reached."); e.Handled = true; } } } }