title: Format Exception
body: <p>The below snipets are  from my Form1 code.  I keep getting a Format Exception because of my MessageBox.Show(…); declaration in my Stop() method.  Why?  What am I doing wrong?
          ...</p>
  
  <pre><code>    private TimeSpan iterationDuration = TimeSpan.Zero;
      ...
  
      public void Stop()
      {
          IsGameOver = true;
          MessageBox.Show(String.Format("Game Over\n\nScore = {0}\n\n Time Duration =   {l}", score, iterationDuration));
          Application.Exit();
      }
  
  
      public void Start()
      {
  
          score = 0;
          IsGameOver = false;
  
          currentRedLightX = 0;
          currentRedLightY = 0;
  
          currentGreenLightX = width / 2;
          currentGreenLightY = height / 2;
  
  
          double minIterationDuration = SPEED; // 50 frames / sec
  
          //game loop
          while (!IsGameOver)
          {
              if (IsCollision())
              {
                  score += 10;
              }
  
              DateTime startIterationTime = System.DateTime.Now;
              UpdateGameState();
              Render();
              DateTime endIterationTime = System.DateTime.Now;
              TimeSpan iterationDuration = endIterationTime - startIterationTime;
              if (iterationDuration.TotalMilliseconds &lt; minIterationDuration)
                  Thread.Sleep(Convert.ToInt32(minIterationDuration - iterationDuration.TotalMilliseconds));
              Application.DoEvents();
          }
  
      }
  </code></pre>