Значение “maxValue” должно быть больше нуля C#

Учу с книжки, пытаюсь запустить код – не работает, ошибка в методе AddEnemy(), подскажите пожалуйста, как исправить генерацию случайной высоты, чтоб заработало.

using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks; 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;  using System.Windows.Media.Animation;  namespace Save_the_Humans {     /// <summary>     /// Interaction logic for MainWindow.xaml     /// </summary>     public partial class MainWindow : Window     {         Random random = new Random();         public MainWindow()         {             InitializeComponent();         }          private void StartButton_Click(object sender, RoutedEventArgs e)         {             AddEnemy();         }          private void AddEnemy()         {             ContentControl enemy = new ContentControl();             enemy.Template = Resources["EnemyTemplate"] as ControlTemplate;             AnimateEnemy(enemy, 0, playArea.ActualWidth - 100, "(Canvas.Left)");             AnimateEnemy(enemy, random.Next((int)playArea.ActualHeight - 100),                 random.Next((int)playArea.ActualHeight - 100), "(Canvas.Top)");             playArea.Children.Add(enemy);          }          private void AnimateEnemy(ContentControl enemy, double from, double to, string propertyToAnimate)         {             Storyboard storyboard = new Storyboard() { AutoReverse = true, RepeatBehavior = RepeatBehavior.Forever };             DoubleAnimation animation = new DoubleAnimation()             {                 From = from,                 To = to,                 Duration = new Duration(TimeSpan.FromSeconds(random.Next(4, 6))),             };             Storyboard.SetTarget(animation, enemy);             Storyboard.SetTargetProperty(animation, new PropertyPath(propertyToAnimate));             storyboard.Children.Add(animation);             storyboard.Begin();         }     } }