If it is outside it finds it OK? Thoughts.....
See XMAL below
<
Grid x:Name="LayoutRoot">
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition Height="*" />
<RowDefinition Height="Auto" />
</Grid.RowDefinitions>
<!--Header Region -->
<Grid Grid.Row="0" HorizontalAlignment="Stretch" VerticalAlignment="Stretch">
<!--<ContentControl x:Name="HeaderRegionContentControl" cal:RegionManager.RegionName="HeaderRegion" ></ContentControl>-->
<StackPanel Grid.Column="1" HorizontalAlignment="Right" Margin="4" Orientation="Horizontal">
<Button Content="Search Customers" Width="120" Height="22" Click="OnSearchCustomers"/>
<Button Content="Search Contacts" Width="120" Height="22" Click="OnSearchContacts"/>
</StackPanel>
</Grid>
<radDock:RadDocking x:Name="radDocking" Grid.Row="1">
<radDock:RadDocking.DocumentHost>
<radDock:RadSplitContainer>
<radDock:RadPaneGroup x:Name="radMainGroup">
<radDock:RadDocumentPane Title="Main Content Region" CanFloat="False" CanUserClose="False">
<radDock:RadDocumentPane.Content>
Region Manager will not find this
<ContentControl x:Name="MainContentControl" cal:RegionManager.RegionName="MainContentRegion"></ContentControl>
</radDock:RadDocumentPane.Content>
</radDock:RadDocumentPane>
</radDock:RadPaneGroup>
</radDock:RadSplitContainer>
</radDock:RadDocking.DocumentHost>
<radDock:RadSplitContainer radDock:DockingPanel.InitialSize="235,235" MaxWidth="600" Name="LeftContainer" InitialPosition="DockedLeft">
<radDock:RadPaneGroup x:Name="Group1">
<radDock:RadPane x:Name="PanelTreeView" Header="Document Explorer" CanDockInDocumentHost="False" CanUserClose="False" CanFloat="False">
<!--<ContentControl x:Name="NavigationContentControl" cal:RegionManager.RegionName="NavigationRegion" ></ContentControl>-->
</radDock:RadPane>
</radDock:RadPaneGroup>
</radDock:RadSplitContainer>
</radDock:RadDocking>
<StackPanel Grid.Row="2" HorizontalAlignment="Left" Orientation="Horizontal">
<TextBlock Text="Status Bar" Margin="2"/>
</StackPanel>
</Grid>