title: WPF xmlns: The 'clr-namespace' URI refers to a namespace that is not included in the assembly
body: <p>I am learning data binding in xaml and this xmlns problem is stopping me. My cs code is in namespace "Ping". Here is my MainWindow.xaml:</p>
  
  <pre><code>&lt;Window x:Class="Ping.MainWindow"
      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
      xmlns:custom="clr-namespace:WPFDemo;assembly=WPFDemo"
      xmlns:local="clr-namespace:Ping"
  </code></pre>
  
  <p>The last line complains as in the title. Why is it not working? I am using "Ping" and it's the only namespace I got.</p>
  
  <p>Thanks</p>