title: Strange exception in Prism application
body: <p>I am trying to get a Prism application to start up, and am getting a very strange error:</p>
  
  <blockquote>
    <p>InvalidOperationException: ServiceLocationProvider must be set.</p>
  </blockquote>
  
  <p>I am using <code>MainWindow</code> in the main (module host) application as the region for a single main shell, that has it's own regions. That way I can swap out main window layouts if needed.</p>
  
  <p>I get the error on the <code>InitializeComponent();</code> call, the only line of code in the constructor  of <code>MainWindow</code>. Google and Bing both return zero results for that exact phrase.</p>
  
  <p>The XAML element in <code>MainWindow</code> is:</p>
  
  <pre><code>&lt;ContentControl regions:RegionManager.RegionName="MainShellRegion" /&gt;
  </code></pre>
  
  <p>Do I have to implement some interface or something on <code>MainWindow</code> to solve this? I am completely stumped.</p>