Scroll bar of the textblock not working

Question

If you notice belowTextblock is wrapped in ScrollViewer control but the scrolling doesnt seem to work. Please see the code below

  <StackPanel Orientation="Vertical" Margin="5,29,5,10" Width="295"  VerticalAlignment="Stretch">

            <Image Name="imgInventory" Stretch="Fill" Height="118" VerticalAlignment="Top" DockPanel.Dock="Right" Margin="10,0"/>

            <ScrollViewer Name="Contentscroll">

                <TextBlock Name="txtDescription" Height="146" TextWrapping="Wrap" Padding="0,2,0,2" Margin="0,0,10,0" ScrollViewer.HorizontalScrollBarVisibility="Auto"

                  ScrollViewer.VerticalScrollBarVisibility="Auto" ScrollViewer.CanContentScroll="True" ></TextBlock>

            </ScrollViewer>

            <Border CornerRadius="6"

                BorderBrush="Gray"

                BorderThickness="2"

                Padding="8" Height="182" Margin="0,0,10,0">

                  <Grid  Height="158"   >

                    <Grid.ColumnDefinitions>

                    <ColumnDefinition Width="Auto"></ColumnDefinition>

                    <ColumnDefinition Width="86"></ColumnDefinition>

                        <ColumnDefinition Width="86"></ColumnDefinition>

                </Grid.ColumnDefinitions>

                <Grid.RowDefinitions >

                    <RowDefinition Height="Auto"></RowDefinition>

                    <RowDefinition Height="Auto"></RowDefinition>

                    <RowDefinition Height="Auto"></RowDefinition>

                    <RowDefinition Height="Auto"></RowDefinition>

                    <RowDefinition Height="Auto"></RowDefinition>

                    <RowDefinition Height="Auto"></RowDefinition>

                    </Grid.RowDefinitions>

                <Label Grid.Row="0" Grid.Column="0">Type:</Label>

                <Label Name="lblType" Grid.Row="0" Grid.Column="1">Type:</Label>

                <Label Grid.Row="1" Grid.Column="0">Make:</Label>

                <Label Name="lblMake" Grid.Row="1" Grid.Column="1"></Label>

                <Label Grid.Row="2" Grid.Column="0">Model:</Label>

                <Label Name="lblModel" Grid.Row="2" Grid.Column="1"></Label>

                <Label Name="lblNoOfWheels" Grid.Row="3" Grid.Column="0">No of Wheels:</Label>

                <Label Name="lblNo_Of_Wheels" Grid.Row="3" Grid.Column="1">Type:</Label>

                <Label Grid.Row="4" Grid.Column="0">Road Vehicle:</Label>

                <Label Name="lblRoadVehicle" Grid.Row="4" Grid.Column="1">Type:</Label>

                <Label Grid.Row="5" Grid.Column="0">Quantity:</Label>

                    <TextBox Name="txtQuantity" Grid.Row="5" Margin="7,0,0,0" Grid.Column="1" HorizontalAlignment="Left" Width="33" />

                <Button Name="btnEdit" Content="Edit" Grid.Column="2" HorizontalAlignment="Left" Margin="14,0,0,3" Grid.Row="5" Width="46" RenderTransformOrigin="-0.027,0.5" Height="20" VerticalAlignment="Bottom" Click="btnEdit_Click"/>

                </Grid>

                </Border>

                

            </StackPanel>