How can I change label content at runtime on a window with a storyboard running? (.NET 3.5)

My Main Window opens a dialog that displays a progress spinner storyboard and should update the content of the labels as the program does some work, but I can't seem to change the label content on that dialog during runtime.

I'm familiar with background workers and the dispatcher, I've been able to update controls before, i.e.:

                main.label_Connected.Dispatcher.Invoke(
                DispatcherPriority.Normal,
                (ThreadStart)delegate { main.label_Connected.Content = "Not Connected"; }
            );

but it doesn't work in this case.  Is there something specific to updating controls when there is a storyboard running?