New Post: PropertyGrid custom type error

What is not working ?
From using your code snippet, I build a working sample.
Upon executing, I can see the propertyGrid with 1 property displaying its editor as you defined it in XAML.

<Window x:Class="WpfApplication4.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:xctk="http://schemas.xceed.com/wpf/xaml/toolkit"
        xmlns:local="clr-namespace:WpfApplication4"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525">
   <Grid>
      <xctk:PropertyGrid x:Name="_propertyGrid"
                         SelectedObject="{Binding}">
         <xctk:PropertyGrid.EditorDefinitions>
            <xctk:EditorTemplateDefinition>
               <xctk:EditorTemplateDefinition.TargetProperties>
                  <xctk:TargetPropertyType Type="{x:Type local:myClass}" />
               </xctk:EditorTemplateDefinition.TargetProperties>
               <xctk:EditorTemplateDefinition.EditingTemplate>
                  <DataTemplate>
                     <Grid VerticalAlignment="Center"
                           HorizontalAlignment="Stretch">
                        <Grid.ColumnDefinitions>
                           <ColumnDefinition Width="*" />
                           <ColumnDefinition Width="Auto" />
                        </Grid.ColumnDefinitions>
                        <TextBlock  Background="{Binding Value.Brush}"
                                    Text="{Binding Value.Name}" />
                        <Button  Grid.Column="1"
                                 Content=". . ."
                                 FontSize="9"
                                 FontWeight="Bold"
                                 VerticalAlignment="Top"
                                 Width="25"
                                 Height="15"/>
                     </Grid>
                  </DataTemplate>
               </xctk:EditorTemplateDefinition.EditingTemplate>
            </xctk:EditorTemplateDefinition>
         </xctk:PropertyGrid.EditorDefinitions>
      </xctk:PropertyGrid>
   </Grid>
</Window>

  public partial class MainWindow : Window
  {
    public MainWindow()
    {
      InitializeComponent();
      this.DataContext = new ContextClass();
    }   
  }

  public class ContextClass
  {
    public ContextClass()
    {
      this.MyObject = new myClass() { Brush = Brushes.Green, Name = "Bob" };
    }

    public myClass MyObject
    {
      get;
      set;
    }
  }

  public class myClass : DependencyObject
  {
    public static readonly DependencyProperty BrushProperty = DependencyProperty.Register( "Brush", typeof( Brush ), typeof( myClass ) );
    public Brush Brush
    {
      get
      {
        return ( Brush )GetValue( BrushProperty );
      }
      set
      {
        SetValue( BrushProperty, value );
      }
    }

    public static readonly DependencyProperty NameProperty = DependencyProperty.Register( "Name", typeof( string ), typeof( myClass ) );
    public string Name
    {
      get
      {
        return ( string )GetValue( NameProperty );
      }
      set
      {
        SetValue( NameProperty, value );
      }
    }
  }