Tooltip is not visble on the disabled checkbox wpf

Tooltip is not visible on disabled checkbox even after setting ToolTipService.ShowOnDisabled="True".

<CheckBox Grid.Column="0" HorizontalAlignment="Center" Visibility="{Binding Converter={StaticResource TaskCompletionVisbilityConverter},ConverterParameter='chkbox'}" 
                             Height="16" Width="16" Foreground="{Binding Converter={StaticResource TaskColorConverter}}"
                               ToolTipService.ShowOnDisabled="True" ToolTipService.IsEnabled="True"
                              ToolTip="Check To complete Task"
                               IsEnabled="{Binding State, Converter={StaticResource EnableDisableConverter},
                        ConverterParameter='checkbox',Mode=TwoWay}" Margin="37,5,0,0">