title: ManualResetEvent WaitOne not unblocking
body: <p>I'm a little confused over a ManualResetEvent that I'm using which doesn't appear to be unblocking. Anyone know why this might be the case?</p>
  
  <p>The scenario I've got is something along these lines. The real situation is quite complicated and I've not managed to isolate a section of code that's reasonable to post to reproduce the issue.</p>
  
  <p><strong>EDIT</strong><br>
  I've updated the code example below. This is execute in a number of different dialogs and I have noticed that one of them hits the this.mre.WaitOne(); Then what happens is I get a "Server Busy" dialog, where I need to press 'switch to' or 'retry', which will then allow my code to step passed the WaitOne() call and all will work. I'm not sure how its relevant, but obviously its of some important.</p>
  
  <pre><code>public class A
  {
   ManualResetEvent mre;
  
   public void Start(ThreadClass tc)
   {
      this.mre = new ManualResetEvent(false);
      tc.Begin();
  
      WebClient wc = new WebClient();
      // progress events are pumped to the ThreadClass which then update the Form2.
      wc.DownloadFileCompleted += new System.ComponentModel.AsyncCompletedEventHandler(wc_DownloadFileCompleted);
  
      wc.DownloadFileAsync("Src", "Tgt");
      this.mre.WaitOne();
   }
  
   void void wc_DownloadFileCompleted(object sender, System.ComponentModel.AsyncCompletedEventArgs e)
   {
      try
      {
       // Do Stuff
      }
      finally
      {
        this.mre.Set();
      }
   }
  }
  
  public class ThreadClass
  {
     Begin()
     {
        Thread t = new Thread(new ThreadStart(DoWork));
        t.Start();
     }
  
     private void DoWork()
     {
       Form f = new Form2();
       f.ShowDialog();
  
       // Sits waiting on another ResetEvent to determine when to close the thread.
     }
  }
  </code></pre>