<ControlTemplate x:Key="validationTemplate">
  <DockPanel>
    <TextBlock Foreground="Red" FontSize="20">!</TextBlock>
    <AdornedElementPlaceholder/>
  </DockPanel>
</ControlTemplate>

public class myErorrTemplate : ControlTemplate
    {
        public myErorrTemplate()
        {
            FrameworkElementFactory dp = new FrameworkElementFactory(typeof(DockPanel));
            FrameworkElementFactory txt = new FrameworkElementFactory(typeof(TextBlock));
            txt.SetValue(TextBlock.ForegroundProperty, Brushes.Red);
            txt.SetValue(TextBlock.TextProperty, "adfdfgdf");
            AdornedElementPlaceholder a = new AdornedElementPlaceholder();
            dp.AppendChild(txt);
            this.VisualTree = dp;
        }
    }

ResourceDictionary resDic = new ResourceDictionary() { Source = new Uri("pack://application:,,/Prog/XAML/Dictionary.xaml") };
txtBox.Style = (Style)resDic["ErrorStyleBottom"];  

<Style x:Key = "ErrorStyleBottom">
        <Setter Property = "Validation.ErrorTemplate">
            <Setter.Value>
                <ControlTemplate>
                    <DockPanel LastChildFill = "True">
                        <TextBlock DockPanel.Dock = "Bottom"
                        Foreground = "Red"
                        FontSize = "10pt"                        
                        Text = "{Binding ElementName=MyAdorner,Path=AdornedElement.(Validation.Errors)[0].ErrorContent}">
                        </TextBlock>                                                                            
                        <AdornedElementPlaceholder Name = "MyAdorner" />
                    </DockPanel>                    
                </ControlTemplate>
            </Setter.Value>
        </Setter> 
        <Setter Property="Control.Margin" Value="0,2,0,0"/>
        <Style.Triggers>
            <Trigger Property="Validation.HasError" Value="true">
                <Setter Property="Control.Margin" Value="0,2,0,20"></Setter>               
            </Trigger>
        </Style.Triggers>
    </Style>