title: the property 'Content' is set more than once
body: <p>I am having the following XAML code, which throws error following error pointing to line# 16.</p>
  
  <blockquote>
    <p>the property 'Content' is set more
    than once</p>
  </blockquote>
  
  <p>Any thoughts?</p>
  
  <pre><code>1       &lt;Grid x:Name="LayoutRoot" Width="970" Height="460" Background="White"&gt;  
  2           &lt;Grid.RowDefinitions&gt;  
  3               &lt;RowDefinition Height="*"/&gt;
  4               &lt;RowDefinition Height="80"/&gt;
  5           &lt;/Grid.RowDefinitions&gt;
  6           &lt;Border Margin="3" BorderBrush="#FF464646" BorderThickness="1" CornerRadius="5" Grid.Row="0"&gt;
  7               &lt;Border.Background&gt;
  8                   &lt;LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0"&gt;
  9                       &lt;GradientStop Color="#FF5B5A5A" Offset="0.02"/&gt;
  10                      &lt;GradientStop Color="#FF3B3B3B" Offset="0.213"/&gt;
  11                      &lt;GradientStop Color="#FF535151" Offset="0.807"/&gt;
  12                  &lt;/LinearGradientBrush&gt;
  13              &lt;/Border.Background&gt;
  14   
  15               &lt;Liquid:Viewer Content="Viewer"&gt;
  16                   &lt;Image Source="Images/planet.jpg" Opacity="0.8" Stretch="Fill" /&gt;
  17               &lt;/Liquid:Viewer&gt;
  18   
  19           &lt;/Border&gt;
  20          &lt;Border Margin="3" BorderThickness="1" CornerRadius="5" Grid.Row="1"&gt;
  21              &lt;Border.Background&gt;
  </code></pre>