WPF Datagrid style issue with Row validation

HI,

I have data grid and style like this below: 

Issue is: If I apply style to daatgrid then my RowValidationErrorTemplate does not work. i don't see that error icon and If I remove style then it works.

How would i solve that?

Data Grid

<loc:RhinoDataGrid Grid.Row="0"  VirtualizingStackPanel.IsVirtualizing="False" ItemsSource="{Binding DataTable, Mode=TwoWay}">        

            <DataGrid.RowValidationRules>
                <loc:CourseValidationRule ValidationStep="RawProposedValue"/>
            </DataGrid.RowValidationRules>
            <DataGrid.RowValidationErrorTemplate>
                <ControlTemplate>
                    <Grid Margin="0,-2,0,-2">
                        <Ellipse StrokeThickness="0" Fill="Red" 
              Width="{TemplateBinding FontSize}" 
              Height="{TemplateBinding FontSize}" />
                        <TextBlock Text="!" FontSize="{TemplateBinding FontSize}" 
              FontWeight="Bold" Foreground="White" 
              HorizontalAlignment="Center"  />
                    </Grid>
                </ControlTemplate>
          </DataGrid.RowValidationErrorTemplate>

  </loc:RhinoDataGrid>

Datagrid Style

<Window.Resources>
        <!-- Control template for row header -->
        <ControlTemplate TargetType="{x:Type DataGridRowHeader}" x:Key="RowHeaderControlTemplate">
            <Grid Background="{TemplateBinding Background}" x:Name="dgRowHeader">
                <Border x:Name="border" BorderThickness="{TemplateBinding BorderThickness}" BorderBrush="{TemplateBinding BorderBrush}"  Grid.ColumnSpan="1">
                    <Rectangle Margin="3,3,3,3" HorizontalAlignment="Stretch" RadiusX="5" RadiusY="5" x:Name="PART_RectangleRow"/>
                </Border>
                <ContentPresenter x:Name="content"  HorizontalAlignment="Center" VerticalAlignment="Center" Content="{TemplateBinding Content}" />
            </Grid>
        </ControlTemplate>

        <Style x:Key="MyDataGridStyle" TargetType="{x:Type DataGrid}">
            <Style.Resources>
                <!--DataGridRowHeader default style-->
                <Style TargetType="{x:Type DataGridRowHeader}">
                    <Setter Property="Width" Value="36" />
                    <Setter Property="BorderBrush" Value="Black"/>
                    <Setter Property="Background" Value="Transparent"/>
                    <Setter Property="BorderThickness" Value="0,0,1,1"/>
                    <Setter Property="Content" Value="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type DataGridRow}}, Converter={StaticResource RowNameConverter}}"/>
                    <Setter Property="Template" Value="{StaticResource RowHeaderControlTemplate}" />
                </Style>
            </Style.Resources>
        </Style>
    </Window.Resources>

Please help

Thanks

Dee