Scrollbars don't appear

Hi!
I would like that when i move a node to the bounds of the diagram the diagram area expands and a scrollbar appear. The problem is that i can’t make the scroolbars appear…
Can someone help me with this issue?
Thanks,

Ricardo

Here is my Xaml code for diagram :

<ScrollViewer HorizontalScrollBarVisibility="Auto" VerticalScrollBarVisibility="Auto" Grid.Row="2" Grid.RowSpan="2" Grid.Column="2" Grid.ColumnSpan="2" FlowDirection="LeftToRight" IsManipulationEnabled="True"> <go:Diagram x:Name="myDiagram" Padding="10" InitialScale="0.75" InitialPanelSpot="MiddleTop" InitialDiagramBoundsSpot="0.5 0 50 0" HorizontalContentAlignment="Stretch" VerticalContentAlignment="Stretch" NodeTemplateDictionary="{StaticResource NodeTemplateDictionary}" LinkTemplate="{StaticResource Link}" Background="#303030" AllowGroup="True" AllowUngroup="True" PreviewMouseMove="myDiagram_PreviewMouseMove" LinkDrawn="myDiagram_LinkDrawn" LinkRelinked="myDiagram_LinkRelinked" SelectionDeleting="myDiagram_SelectionDeleting" GridVisible="False" GridSnapEnabled="False" AllowClipboard="True" AllowCopy="True" >