MVVM Light Messaging Property Change Message Null Reference Exception

On a current project I am using MVVM light framework within WPF.  I love the framework and it has worked great.
But, in software development there is no silver bullet.  So here is a issue I ran across when using the property change message.

Null Reference exception on the receiver.

In my publisher view model I had the following property

  public String MyProperty  
     {  
       get { return _myProperty; }  
       set  
       {  
         if (value == _myProperty) return;  
         var oldValue = _myProperty;  
         _myProperty= value;  
         RaisePropertyChanged("MyProperty", oldValue, value, true);  
       }  
     }  
     private _myProperty;  

In the reciever view Model I Registered and handled the message

 Messenger.Default.Register<PropertyChangedMessage<MyObject>>(this,HandlePropertyChanged);  

  private void HandlePropertyChanged(PropertyChangedMessage<MyObject> propertyChangedMessage)  
     {  
       if (propertyChangedMessage.PropertyName != "MyProperty") return;  
       if( propertyChangedMessage.NewValue != null)        
         JobNumber = propertyChangedMessage.NewValue;        
     }  

In the app.xaml.cs I added
DispatcherHelper.Initialize();

No more null reference exception.