WPF guru Josh Smith has just put up a great post here about how to access the validation errors on a WPF control without getting lots of binding debug output. Most samples (including MSDN documentation) suggest you should use Validation.Errors[0] which generate debug output for a binding failure whenever there are no errors (since Errors[0] doesn’t exist).

The format of the template that I commonly use (which also avoids the Errors[0] issue in almost exactly the same way) is as follows:

        <ControlTemplate x:Key="DefaultErrorTemplate">
            <DockPanel DataContext="{Binding ElementName=adorner, 
                                                               Path=AdornedElement.(Validation.Errors)/ErrorContent}">
                <Ellipse x:Name="Ellipse" 
                            DockPanel.Dock="Right" 
                            Margin="2,0,2,0" 
                            Width="14" Height="14" 
                            VerticalAlignment="Center" 
                            Stroke="#40000000" StrokeThickness="2" Fill="Red">
                    <Ellipse.ToolTip>
                        <Border MaxWidth="350">
                            <ContentControl FontSize="14" Content="{Binding}"/>
                        </Border>
                    </Ellipse.ToolTip>
                </Ellipse>
                <Border BorderBrush="#40FFAF00" BorderThickness="2" IsHitTestVisible="False">
                    <Border.Background>
                        <SolidColorBrush Color="Red" Opacity="0.2"/>
                    </Border.Background>
                    <AdornedElementPlaceholder Margin="-2" Name="adorner"/>
                </Border>
            </DockPanel>
        </ControlTemplate>

Normally instead of hard coding the colours I would use a colour converter that maps the severity of the error (through a custom property) to the relevant colour, e.g. error=red, warning=orange etc.

My equivalent of Josh’s sample project is here.