<Popup
   PlacementTarget="{Binding ElementName=MainTreeView}"
   IsOpen="{Binding IsOpenErrorWindow}"
   Width="{Binding ElementName=MainTreeView, Path=ActualWidth, Converter={StaticResource Int32MinusValueConverter}, ConverterParameter=20}"
   HorizontalOffset="10"
   MaxHeight="250"
   VerticalOffset="{Binding RelativeSource={RelativeSource Self}, Path=ActualHeight, Converter={StaticResource Int32NegativeMinusValueConverter}, ConverterParameter=10}"
   AllowsTransparency="True" PopupAnimation="Fade">