ChildWindow: fixed bug in the .NET 3.5 version when setting the FocusVisualStyle in the OnApplyTemplate method. .NET 3.5 doesn't support setting Setter.Value with a ContentControl so it is a limitation of the .net framework. Luckily this works in .NET 4.0. The work around was to not use a focus visual style in the .NET 3.5 version and to set it to null.

ExtendedWPFToolkitSolution/Src/WPFToolkit.Extended/ChildWindow/Implementation/ChildWindow.cs

@@ -430,6 +430,9 @@ namespace Microsoft.Windows.Controls
 
             _root = GetTemplateChild("Root") as Grid;
 
+#if VS2008
+            FocusVisualStyle = null;
+#else
             Style focusStyle = _root.Resources["FocusVisualStyle"] as Style;
             if (focusStyle != null)
             {
@@ -437,7 +440,7 @@ namespace Microsoft.Windows.Controls
                 focusStyle.Setters.Add(focusStyleDataContext);
                 FocusVisualStyle = focusStyle;
             }
-
+#endif
             _root.Children.Add(_modalLayerPanel);
         }