title: ValidationSummary does not exist in WPF?
body: <p>I'm trying to Style a WPF DataGrid.  I copied the Control Template from <a href="http://msdn.microsoft.com/en-us/library/cc278066%28v=vs.95%29.aspx" rel="nofollow">here</a>, into a resource dictionary.  I can't get it to compile, because it says, </p>
  
  <p>"ValidationSummary does not exist in XML namespace"</p>
  
  <p>I have all the PresentationCore and PresentationFramework assemblies referenced in my project.</p>
  
  <p>I think I might need "System.Windows.Controls.Data.Input.dll" but I can't find it.</p>