Why is HttpNotificationChannel.Open throwing ArgumentException() E_INVALIDARG?

Question

Here is my code. Everything works fine the first time I run it, i.e. HttpNotificationChannel.Find() returns null.

But the second time I run it, Find() returns the proper thing, however when I get to the Open() call, it throws an exception. Which is really odd, since Open() doesn't take any arguments.

What am I doing wrong?

  public string ChannelName = "MyAppChannel";
  ...
  NotificationChannel = HttpNotificationChannel.Find(ChannelName);
  if (NotificationChannel == null)
  {
    NotificationChannel = new HttpNotificationChannel(ChannelName);
  }
  NotificationChannel.ChannelUriUpdated += new EventHandler(Channel_ChannelUriUpdated);
  NotificationChannel.HttpNotificationReceived += new EventHandler(NotificationChannel_HttpNotificationReceived);
  NotificationChannel.ErrorOccurred += new EventHandler(Channel_ErrorOccurred);
  NotificationChannel.Open();         // <-- Kaboom here, the 2nd time 

Here's the full text and stack:

System.ArgumentException: E_INVALIDARG
   at Microsoft.Phone.Notification.SafeNativeMethods.ThrowExceptionFromHResult(Int32 hr, Exception defaultException, NotificationType type)
   at Microsoft.Phone.Notification.HttpNotificationChannel.Open()
   at LiveShare.NotificationManager.Initialize()
   at LiveShare.App..ctor()
   at System.Reflection.RuntimeConstructorInfo.InternalInvoke(RuntimeConstructorInfo rtci, BindingFlags invokeAttr, Binder binder, Object parameters, CultureInfo culture, Boolean isBinderDefault, Assembly caller, Boolean verifyAccess, StackCrawlMark& stackMark)
   at System.Reflection.RuntimeConstructorInfo.InternalInvoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, StackCrawlMark& stackMark)
   at System.Reflection.ConstructorInfo.Invoke(Object[] parameters)
   at MS.Internal.TypeProxy.<>c__DisplayClass30.b__2a()
   at MS.Internal.TypeProxy.CreateInstance(UInt32 customTypeId)
   at MS.Internal.FrameworkCallbacks.CreateKnownObject(IntPtr nativeRootPeer, UInt32 customTypeId, String initializationString, IntPtr& nativePeer, UInt32 isCreatedByParser)
   at MS.Internal.FrameworkCallbacks.CreateUnknownObject(String assemblyName, String typeName, IntPtr nativeRootPeer, String initializationString, UInt32& customTypeId, UInt32& coreTypeId, UInt32& typeFlags, IntPtr& nativePeer)

Answer 1

The correct solution is not to call Open() if Find() succeeds.

Answer 2

This looks very similar to a documented problem with the CTP as described by Nick Harris last April.

Solution: If you try to Open a channel almost immediately after you hit Debug when emulator fires up this issue will occur. The solution is simple – Give the emulator two minutes before making the call.

In case that's not it, there's a good article on Silverlight Show that covers push notifications in a WP7 stock quote app.