title: WPF root element is not valid for navigation
body: <p>I am converting a WPF XBAP app to a WPF desktop app.  I have it running on the desktop, but am now trying to change the Page references to Window references.  </p>
  
  <pre><code>'MyApp.StartForm' root element is not valid for navigation.
  </code></pre>
  
  <p>I have tried creating a simple version of this app and converting that, and this works fine, so there must be something within the XAML that is causing this when using Window tags.  My question relates to how I can investigate this.  Currently, all I get is this error, accompanied by a "No Source Available" screen; no stack locations are shown and "Show Disassembly" doesn't work.  Other than systematically commenting out individual chunks of XAML until it works, is there a way to work out what this issue is?</p>