"Telerik Docking"控件使用发生错误

Question

"Telerik Docking"控件使用发生错误。

用“ExpressionBlend”拖动“RadDocking”到“操作面板”，发生错误，信息如下：

对应XAML如下：

<UserControl xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
  xmlns:telerikDocking="clr-namespace:Telerik.Windows.Controls;assembly=Telerik.Windows.Controls.Docking"
x:Class="TelerikDockingTest.MainPage"
Width="640" Height="480">

<Grid x:Name="LayoutRoot" Background="White">
<telerikDocking:RadDocking HasDocumentHost="True" HorizontalAlignment="Stretch" VerticalAlignment="Stretch">
<telerikDocking:RadSplitContainer>
<telerikDocking:RadPaneGroup HorizontalAlignment="Stretch">
<telerikDocking:RadPane Header="Pane 1"/>
<telerikDocking:RadPane Header="Pane 2"/>
</telerikDocking:RadPaneGroup>
</telerikDocking:RadSplitContainer>
</telerikDocking:RadDocking>
</Grid>
</UserControl>

这是什么错误？？？

根据“官方文档”操作的啊，为什么会发生这样的错误？？？

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