protected override void OnNavigatedFrom(NavigationEventArgs e) {
  this.NavigationService.RemoveBackEntry(); //remove itself from the backStack
  base.OnNavigatedFrom(e);
}

In particular for a LoginPage (if it is not implemented as a popup window or a section of the MainPage hidden/visible properly), if the login is not always requiìred but depends from some configuration settings (ex. once a day login) it is convinent to call first the MainPage, check if the user is already authenticated in the _load method and if not call the LoginPage. A convenient flag can be used to discriminate in the OnNavigatedFrom method of the MainPage if the LoginPage is called or not and so eventually use the NavigationService.RemoveBackEntry().

void MainPage_Loaded(object sender, RoutedEventArgs e) {
  if (!DataSourceManager.LoginDataSource.User.Authenticated) {
    //if the user is not authenticated, let's go to the LoginPage
    NavigationService.Navigate(new Uri("/LoginPage.xaml", UriKind.Relative));
    toLoginflag = true;
  } else {
    Main.Visibility = System.Windows.Visibility.Visible;
  }
}

protected override void OnNavigatedFrom(NavigationEventArgs e) {
  if (toLoginflag) {
    this.NavigationService.RemoveBackEntry(); //remove itself from the backStack
  }
}

public static ProgressIndicator progInd = newProgressIndicator();

and in the constructor add:

progInd.IsIndeterminate = false; progInd.IsVisible = false;

Then add in the page where you need the progressBar a method like this:

privatevoid RunProgressBar(bool value) {
  if (value) {
    App.progInd.Text = LocalizedStrings.GetString(“Loading”);
    App.progInd.IsIndeterminate = true;
    App.progInd.IsVisible = true;
    SystemTray.SetProgressIndicator(this, App.progInd);
  }
  else {
    App.progInd.Text = null;
    App.progInd.IsIndeterminate = false;
    App.progInd.IsVisible = false;
    SystemTray.SetProgressIndicator(this, null);
  }
}

if(e.NavigationMode == NavigationMode.New) { //it is called for the first time

Remember that the OnNavigationTo method is called just after the page contructor and befor the possible MyPage_Load method, if you define that new RoutedEventHandler in the page contructor

 this.Loaded += newRoutedEventHandler(MyPage_Loaded);) 

                        <CheckBox x:Name="checkBoxMergeAudio" IsChecked="{Binding IsMergeAudio, Mode=TwoWay}" Margin="0,0,0,0" Click="checkBoxMergeAudio_Changed" ClickMode="Release">
                            <TextBlock TextWrapping="Wrap" Text="{Binding LocalizedResources.MergeAudio, Source={StaticResource LocalizedStrings}}" />
                        </CheckBox>

StringBuilder sbPage = new StringBuilder("/").Append(baseUri);
sbPage.Append("?ID=").Append("&asset=").Append(<strong>Uri.EscapeDataString</strong>(asset.<em>Description</em>));
NavigationService.Navigate(new Uri(sbPage.ToString(), UriKind.Relative));