Parent-Child Grid Issue in wpf

<DataGrid  >
                <DataGrid.Columns>
                    <DataGridTemplateColumn Header="C">
                        <DataGridTemplateColumn.CellTemplate>
                            <DataTemplate>
                                 <StackPanel>
                        <Button x:Name="btnCollapse"  ToolTip="Expand" Foreground="Black" Background="Transparent" BorderBrush="Transparent" Tag="{Binding LineItemKitsID}"   >
                                        <Image Source="../images/Plus.png" Cursor="Hand" Height="20" Width="15" ></Image>
                                    </Button>
                                </StackPanel>
                            </DataTemplate>
                        </DataGridTemplateColumn.CellTemplate>
                    </DataGridTemplateColumn>

                    <DataGridTextColumn CanUserReorder="True" CanUserResize="True" CanUserSort="True" Width="160*" Binding="{Binding GroupName}" Header="Group Name"  Foreground="Black">
                    </DataGridTextColumn>


                </DataGrid.Columns>
    <DataGrid.RowDetailsTemplate>
        <DataTemplate>
            <StackPanel Orientation="Horizontal">
                <DataGrid Name="NestedDG">
                    <DataGrid.Columns>
                        <DataGridTextColumn CanUserReorder="True" CanUserResize="True" CanUserSort="True" Width="230" Binding="{Binding LineItem}" Header="Line Item"  Foreground="Black">
                        </DataGridTextColumn>
                      


                        <DataGridTextColumn CanUserReorder="True" CanUserResize="True" CanUserSort="True" Width="110" Binding="{Binding EffectiveDate}" Header="Effective Date"  Foreground="Black">
                        </DataGridTextColumn>

                       
                   
                    </DataGrid.Columns>

                </DataGrid>
            </StackPanel>
        </DataTemplate>
    </DataGrid.RowDetailsTemplate>

RowDetailsVisibilityChanged

protected void ParentDG_RowDetailsVisibilityChanged(object sender, DataGridRowDetailsEventArgs e)
           {
            DataGrid nestedGrid = (DataGrid)e.DetailsElement.FindName("NestedDG");
              if (e.Row.DetailsVisibility == Visibility.Visible)
              {
                  nestedGrid.ItemsSource = dsKitDetails.Tables[0].DefaultView;
              }

            }