title: Undefined CLR namespace
body: <p>I have the following:</p>
  
  <p><img src="https://i.stack.imgur.com/myPXU.png" alt="Error! Error!"></p>
  
  <p>The error says <strong>The 'clr-namespace' URI refers to a namespace '{0}' that is not included in the assembly.</strong></p>
  
  <p>I've build and rebuild but nothing happens. I'm sure this must work, because a WPF demo app that I downloaded has everything the same. What's going on?</p>