Placing this ScrollViewer throws error - wpf

Question

I have a WPF Window that has a custom border, Thumb controls for resizing, and a two-column layout. The right column (main content area) is a UserControl with a ScrollViewer, so it scrolls as needed. I want to add a ScrollViewer to the left column, but when I do, at runtime it gives me
Initialization of 'System.Windows.Controls.Primitives.ScrollBar' threw an exception.
with an inner exception of
Unable to cast object of type 'MS.Internal.NamedObject' to type 'System.Windows.FrameworkTemplate'.
If I take the ScrollViewer out, everything works fine again.
Here's the basic XAML (with the ScrollViewer wrapped around the TaskPane ItemsControl):
<Window x:Class="MyWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Width="525" MinWidth="200"
Height="350" MinHeight="85"
FontFamily="Segoe UI"
AllowsTransparency="True" Background="Transparent"
ResizeMode="CanResize" WindowStyle="None">
<Border>
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="6"/>
<ColumnDefinition Width="*"/>
<ColumnDefinition Width="6"/>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="6"/>
<RowDefinition Height="*"/>
<RowDefinition Height="6"/>
</Grid.RowDefinitions>
<Grid Grid.Column="1" Grid.Row="1">
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="*"/>
<RowDefinition Height="22"/>
</Grid.RowDefinitions>
<Grid Grid.Row="0">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*"/>
<ColumnDefinition Width="Auto"/>
</Grid.ColumnDefinitions>
<StackPanel Grid.Column="0" Orientation="Vertical">
<TextBlock Name="Caption" Text="My Window"/>
</StackPanel>
<StackPanel Grid.Column="1" Orientation="Vertical">
<!-- Minimize/Maximize/Close buttons -->
</StackPanel>
</Grid>
<Grid Grid.Row="1">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="160"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="24"/>
<RowDefinition Height="*"/>
</Grid.RowDefinitions>
<ScrollViewer Grid.Column="0" Grid.Row="1">
<ItemsControl Name="TaskPane">
...
</ItemsControl>
</ScrollViewer>
<StackPanel Name="MainContent" Grid.Column="1" Grid.Row="1" Orientation="Vertical">
...
</StackPanel>
</Grid>
</Grid>
<ResizeGrip Name="ResizeGrip" Grid.Column="1" Grid.ColumnSpan="2" Grid.Row="1" Grid.RowSpan="2" Foreground="Red" HorizontalAlignment="Right" VerticalAlignment="Bottom" Width="16" Height="16" Padding="0 0 18 18"/>
<Thumb Name="TopLeftThumb" Grid.Column="0" Grid.Row="0" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Opacity="0" Cursor="SizeNWSE" DragDelta="TopLeftThumb_DragDelta"/>
<Thumb Name="TopThumb" Grid.Column="1" Grid.Row="0" VerticalAlignment="Top" Opacity="0" Cursor="SizeNS" DragDelta="TopThumb_DragDelta" />
<Thumb Name="TopRightThumb" Grid.Column="2" Grid.Row="0" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Opacity="0" Cursor="SizeNESW" DragDelta="TopRightThumb_DragDelta"/>
<Thumb Name="LeftThumb" Grid.Column="0" Grid.Row="1" HorizontalAlignment="Left" Opacity="0" Cursor="SizeWE" DragDelta="LeftThumb_DragDelta" />
<Thumb Name="RightThumb" Grid.Column="2" Grid.Row="1" HorizontalAlignment="Right" Opacity="0" Cursor="SizeWE" DragDelta="RightThumb_DragDelta" />
<Thumb Name="BottomLeftThumb" Grid.Column="0" Grid.Row="2" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Opacity="0" Cursor="SizeNESW" DragDelta="BottomLeftThumb_DragDelta"/>
<Thumb Name="BottomThumb" Grid.Column="1" Grid.Row="2" VerticalAlignment="Bottom" Opacity="0" Cursor="SizeNS" DragDelta="BottomThumb_DragDelta" />
<Thumb Name="BottomRightThumb" Grid.Column="2" Grid.Row="2" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Opacity="0" Cursor="SizeNWSE" DragDelta="BottomRightThumb_DragDelta"/>
</Grid>
</Border>
I've searched online, but can find anything on this. I've tried creating another UserControl with a ScrollViewer as the layout root, and get the same error.

Answer 1

By any chance do you have a ScrollViewer style defined in any of your resources somewhere? I saw this link which may be related: http://blog.alner.net/archive/2010/05/07/wpf-style-and-template-resources_order-matters.aspx
The error usually occurs when one style uses a 2nd style, but that 2nd style gets added after the 1st one does. Rather hard error to diagnose.

Answer 2

Don't know if this is the issue, but you didn't set the row and column of the 'StackPanel' after 'ScrollViewer'.