title: Cannot create an instance of "[user control]" error in designer
body: <p>I have created the following user control.  When I add it to a xaml window, I get the error "Cannot create an instance of "ucAppItem".  I dragged the user control onto the window from the toolbar.</p>
  
  <p>XAML of user control is as follows:</p>
  
  <pre><code>&lt;UserControl x:Class="Demos.ucAppItem"
               xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
               xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
               xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
               xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
               mc:Ignorable="d" Width="852" Height="215"&gt;
      &lt;Grid&gt;
  
          &lt;Label Name="lblTitle"  Content="Title" HorizontalAlignment="Left" Margin="233,10,0,0" VerticalAlignment="Top" FontSize="22" FontFamily="Arial"/&gt;
  
  
          &lt;Image Width="40" Height="40" VerticalAlignment="Center" HorizontalAlignment="Right" Margin="0,0,80,0"&gt;
              &lt;Image.Style&gt;
                  &lt;Style TargetType="{x:Type Image}"&gt;
                      &lt;Setter Property="Source" Value="pack://siteoforigin:,,,/arrow2.png"/&gt;
                      &lt;Style.Triggers&gt;
                          &lt;Trigger Property="IsMouseOver" Value="True"&gt;
                              &lt;Setter Property="Source" Value="pack://siteoforigin:,,,/arrow1.png"/&gt;
                          &lt;/Trigger&gt;
                      &lt;/Style.Triggers&gt;
                  &lt;/Style&gt;
              &lt;/Image.Style&gt;
          &lt;/Image&gt;
          &lt;Label x:Name="lblRun" Content="Run" HorizontalAlignment="Right" Margin="0,88,35,0" VerticalAlignment="Top" Foreground="#FF2EAADC" FontSize="20"&gt;
              &lt;Label.Style&gt;
                  &lt;Style TargetType="{x:Type Label}"&gt;
                      &lt;Setter Property="Foreground" Value="#FF2EAADC"/&gt;
                      &lt;Style.Triggers&gt;
                          &lt;Trigger Property="IsMouseOver" Value="True"&gt;
                              &lt;Setter Property="Foreground" Value="#006d9e"/&gt;
                          &lt;/Trigger&gt;
                      &lt;/Style.Triggers&gt;
                  &lt;/Style&gt;
              &lt;/Label.Style&gt;
          &lt;/Label&gt;
      &lt;/Grid&gt;
  &lt;/UserControl&gt;
  </code></pre>
  
  <p>XAML of window is as follows:</p>
  
  <pre><code>&lt;Window
          xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
          xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
          xmlns:local="clr-namespace:Demos" x:Class="Demos.Window1"
          Title="Window1" Height="487" Width="854"&gt;
      &lt;Grid&gt;
  
          &lt;local:ucAppItem/&gt;
  
      &lt;/Grid&gt;
  &lt;/Window&gt;
  </code></pre>
  
  <p>Thanks for your help in advance!</p>