The Printer Refuses to Print a Visual Object

//----------------------------------------------------
// PrintaBunchaButtons.cs (c) 2006 by Charles Petzold
//----------------------------------------------------
using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;
using System.Windows.Media;
namespace Petzold.PrintaBunchaButtons
{
    public class PrintaBunchaButtons : Window
    {
        [STAThread]
        public static void Main()
        {
            Application app = new Application();
            app.Run(new PrintaBunchaButtons());
        }
        public PrintaBunchaButtons()
        {
            Title = "Print a Bunch of Buttons";
            SizeToContent = SizeToContent.WidthAndHeight;
            ResizeMode = ResizeMode.CanMinimize;
            // Create the 'Print' button.
            Button button = new Button();
            button.FontSize = 24;
            button.Content = "Print ...";
            button.Padding = new Thickness(12);
            button.Margin = new Thickness(96);
            button.Click += PrintOnClick;
            Content = button;
        }
        void PrintOnClick(object sender, RoutedEventArgs args)
        {
            PrintDialog printDialog = new PrintDialog();
            if ((bool)printDialog.ShowDialog().GetValueOrDefault())
            {
                // Create the Grid panel.
                Grid grid = new Grid();
                // Define five auto-sized rows and columns.
                for (int i = 0; i < 5; i++)
                {
                    ColumnDefinition columnDefinition = new ColumnDefinition();
                    columnDefinition.Width = GridLength.Auto;
                    grid.ColumnDefinitions.Add(columnDefinition);
                    RowDefinition rowDefinition = new RowDefinition();
                    rowDefinition.Height = GridLength.Auto;
                    grid.RowDefinitions.Add(rowDefinition);
                }
                // Give the Grid a gradient brush.
                grid.Background =
                new LinearGradientBrush(Colors.Gray, Colors.White,
                    new Point(0, 0), new Point(1, 1));
                // Every program needs a little randomness.
                Random random = new Random();
                // Fill the Grid with 25 buttons.
                for (int i = 0; i < 25; i++)
                {
                    Button button = new Button();
                    button.FontSize = 12 + random.Next(8);
                    button.Content = "Button No. " + (i + 1);
                    button.HorizontalAlignment = HorizontalAlignment.Center;
                    button.VerticalAlignment = VerticalAlignment.Center;
                    button.Margin = new Thickness(6);
                    grid.Children.Add(button);
                    Grid.SetRow(button, i % 5);
                    Grid.SetColumn(button, i / 5);
                }
                // Size the Grid.
                grid.Measure(new Size(Double.PositiveInfinity,
                        Double.PositiveInfinity));
                Size gridSize = grid.DesiredSize;
                // Determine the point for centering the Grid on the page.
                Point gridPosition =
                new Point((printDialog.PrintableAreaWidth - gridSize.Width) / 2,
                    (printDialog.PrintableAreaHeight - gridSize.Height) / 2);
                // Layout is complete.
                grid.Arrange(new Rect(gridPosition, gridSize));
                // Now print it.
                printDialog.PrintVisual(grid, Title);
            }
        }
    }
}