Темы в Silverlight Toolkit October убивают валидацию в TextBox. Т.е. валидационный View. Видимо так было раньше и пока так будет, но это несложно поправить.

Если использовать темы из Silverlight Toolkit, то сразу бросается в глаза, что при их применениее сразу убивается View для валидации в TextBox.
Не знаю с чем связано такое безобразие, но вернуть это все несложно. Для этого нужно выполить следующее:

Рассмотрим стандартно применяемые стиль и шаблоны для TextBox на странице TextBox Styles and Templates (En)

Оттуда скопируем в наш файл, взятой из Silverlight Toolkit темы, “ControlTemplate for ValidationTooltip”.
<ControlTemplate x:Key=”ValidationToolTipTemplate”>
…
</ControlTemplate>
Поскольку к этому шаблону из стиля TextBox идет обращение, как к статическому ресурсу по имени ValidationToolTipTemplate, то размещать его XAML надо до XAML стиля TextBox.

Далее нам осталось только дополнить недостающие части XAML стиля для TextBox
<Style TargetType=”TextBox”>
…
</Style>

Сравните аккуратно исходный стиль и стиль в вашей теме и вы легко определите место куда вставить недостающие VisualState’ы и <Border x:Name=”ValidationErrorElement” … >

Для полноты картины я приведу то что должно получиться, а то что быо до этого приведу в следующем посту, тк получается слишком большой объем

Вот что должно получиться:
___________
    <!–TextBox–>
    <!– i!t для TextBox пришлось добавлять (возвращать) разметку и VisualState’s для валидации
    http://iliya-tretyakov.spaces.live.com/blog/cns!6DDCA30C11FA5050!504.entry
    –>
    <ControlTemplate x:Key=”ValidationToolTipTemplate”>
        <Grid x:Name=”Root” Margin=”5,0″ RenderTransformOrigin=”0,0″ Opacity=”0″>
            <Grid.RenderTransform>
                <TranslateTransform x:Name=”xform” X=”-25″/>
            </Grid.RenderTransform>
            <vsm:VisualStateManager.VisualStateGroups>
                <vsm:VisualStateGroup Name=”OpenStates”>
                    <vsm:VisualStateGroup.Transitions>
                        <vsm:VisualTransition GeneratedDuration=”0″/>
                        <vsm:VisualTransition To=”Open” GeneratedDuration=”0:0:0.2″>
                            <Storyboard>
                                <DoubleAnimation Storyboard.TargetName=”xform” Storyboard.TargetProperty=”X” To=”0″ Duration=”0:0:0.2″>
                                    <DoubleAnimation.EasingFunction>
                                        <BackEase Amplitude=”.3″ EasingMode=”EaseOut”/>
                                    </DoubleAnimation.EasingFunction>
                                </DoubleAnimation>
                                <DoubleAnimation Storyboard.TargetName=”Root” Storyboard.TargetProperty=”Opacity” To=”1″ Duration=”0:0:0.2″/>
                            </Storyboard>
                        </vsm:VisualTransition>
                    </vsm:VisualStateGroup.Transitions>
                    <vsm:VisualState x:Name=”Closed”>
                        <Storyboard>
                            <DoubleAnimation Storyboard.TargetName=”Root” Storyboard.TargetProperty=”Opacity” To=”0″ Duration=”0″/>
                        </Storyboard>
                    </vsm:VisualState>
                    <vsm:VisualState x:Name=”Open”>
                        <Storyboard>
                            <DoubleAnimation Storyboard.TargetName=”xform” Storyboard.TargetProperty=”X” To=”0″ Duration=”0″/>
                            <DoubleAnimation Storyboard.TargetName=”Root” Storyboard.TargetProperty=”Opacity” To=”1″ Duration=”0″/>
                        </Storyboard>
                    </vsm:VisualState>
                </vsm:VisualStateGroup>
            </vsm:VisualStateManager.VisualStateGroups>

            <Border Margin=”4,4,-4,-4″ Background=”#052A2E31″ CornerRadius=”5″/>
            <Border Margin=”3,3,-3,-3″ Background=”#152A2E31″ CornerRadius=”4″/>
            <Border Margin=”2,2,-2,-2″ Background=”#252A2E31″ CornerRadius=”3″/>
            <Border Margin=”1,1,-1,-1″ Background=”#352A2E31″ CornerRadius=”2″/>

            <Border Background=”#FFDC000C” CornerRadius=”2″/>
            <Border CornerRadius=”2″>
                <TextBlock
                  UseLayoutRounding=”false”
                  Foreground=”White” Margin=”8,4,8,4″ MaxWidth=”250″ TextWrapping=”Wrap” Text=”{Binding (Validation.Errors)[0].ErrorContent}”/>
            </Border>
        </Grid>
    </ControlTemplate>
    <Style TargetType=”TextBox”>
        <Setter Property=”BorderThickness”
            Value=”1″/>
        <Setter Property=”Background”
            Value=”{StaticResource ShadeBrush}”/>
        <Setter Property=”Foreground”
            Value=”#FF000000″/>
        <Setter Property=”Padding”
            Value=”2″/>
        <Setter Property=”BorderBrush”
            Value=”{StaticResource NormalBorderBrush}” />
        <Setter Property=”Template”>
            <Setter.Value>
                <ControlTemplate TargetType=”TextBox”>
                    <Grid >
                        <vsm:VisualStateManager.VisualStateGroups>
                            <vsm:VisualStateGroup x:Name=”CommonStates”>
                                <vsm:VisualStateGroup.Transitions>
                                    <vsm:VisualTransition GeneratedDuration=”00:00:00.1″
                                        To=”MouseOver”/>
                                    <vsm:VisualTransition GeneratedDuration=”00:00:00.1″
                                        To=”ReadOnly”/>
                                    <vsm:VisualTransition GeneratedDuration=”00:00:00.1″
                                        To=”Disabled”/>
                                    <vsm:VisualTransition From=”Normal”
                                        GeneratedDuration=”00:00:00.3000000″
                                        To=”MouseOver”/>
                                    <vsm:VisualTransition From=”MouseOver”
                                        GeneratedDuration=”00:00:00.5000000″
                                        To=”Normal”/>
                                </vsm:VisualStateGroup.Transitions>
                                <vsm:VisualState x:Name=”Normal”/>
                                <vsm:VisualState x:Name=”MouseOver”>
                                    <Storyboard>
                                        <DoubleAnimationUsingKeyFrames BeginTime=”00:00:00″
                                                   Duration=”00:00:00.0010000″
                                                   Storyboard.TargetName=”HoverBorder”
                                                   Storyboard.TargetProperty=”(UIElement.Opacity)”>
                                            <SplineDoubleKeyFrame KeyTime=”00:00:00″
                                            Value=”1″/>
                                        </DoubleAnimationUsingKeyFrames>
                                    </Storyboard>
                                </vsm:VisualState>
                                <vsm:VisualState x:Name=”Disabled”>
                                    <Storyboard>
                                        <DoubleAnimationUsingKeyFrames Storyboard.TargetName=”DisabledVisualElement”
                                                   Storyboard.TargetProperty=”Opacity”>
                                            <SplineDoubleKeyFrame KeyTime=”0″
                                            Value=”0.6″/>
                                        </DoubleAnimationUsingKeyFrames>
                                    </Storyboard>
                                </vsm:VisualState>
                                <vsm:VisualState x:Name=”ReadOnly”>
                                    <Storyboard>
                                        <DoubleAnimationUsingKeyFrames Storyboard.TargetName=”ReadOnlyVisualElement”
                                                   Storyboard.TargetProperty=”Opacity”>
                                            <SplineDoubleKeyFrame KeyTime=”0″
                                            Value=”1″/>
                                        </DoubleAnimationUsingKeyFrames>
                                    </Storyboard>
                                </vsm:VisualState>
                            </vsm:VisualStateGroup>
                            <vsm:VisualStateGroup x:Name=”FocusStates”>
                                <vsm:VisualStateGroup.Transitions>
                                    <vsm:VisualTransition From=”Focused”
                                        GeneratedDuration=”00:00:00.5000000″
                                        To=”Unfocused”/>
                                    <vsm:VisualTransition From=”Unfocused”
                                        GeneratedDuration=”00:00:00.3000000″
                                        To=”Focused”/>
                                </vsm:VisualStateGroup.Transitions>
                                <vsm:VisualState x:Name=”Focused”>
                                    <Storyboard>

                                        <DoubleAnimationUsingKeyFrames BeginTime=”00:00:00″
                                                   Duration=”00:00:00.0010000″
                                                   Storyboard.TargetName=”FocusVisualElement”
                                                   Storyboard.TargetProperty=”(UIElement.Opacity)”>
                                            <SplineDoubleKeyFrame KeyTime=”00:00:00″
                                            Value=”1″/>
                                        </DoubleAnimationUsingKeyFrames>

                                    </Storyboard>
                                </vsm:VisualState>
                                <vsm:VisualState x:Name=”Unfocused”>
                                    <Storyboard>
                                        <DoubleAnimationUsingKeyFrames BeginTime=”00:00:00″
                                                   Duration=”00:00:00.0010000″
                                                   Storyboard.TargetName=”FocusVisualElement”
                                                   Storyboard.TargetProperty=”(UIElement.Opacity)”>
                                            <SplineDoubleKeyFrame KeyTime=”00:00:00″
                                            Value=”0″/>
                                        </DoubleAnimationUsingKeyFrames>
                                    </Storyboard>
                                </vsm:VisualState>
                            </vsm:VisualStateGroup>

                            <vsm:VisualStateGroup x:Name=”ValidationStates”>
                                <vsm:VisualState x:Name=”Valid”/>
                                <vsm:VisualState x:Name=”InvalidUnfocused”>
                                    <Storyboard>
                                        <ObjectAnimationUsingKeyFrames Storyboard.TargetName=”ValidationErrorElement” Storyboard.TargetProperty=”Visibility”>
                                            <DiscreteObjectKeyFrame KeyTime=”0″>
                                                <DiscreteObjectKeyFrame.Value>
                                                    <Visibility>Visible</Visibility>
                                                </DiscreteObjectKeyFrame.Value>
                                            </DiscreteObjectKeyFrame>
                                        </ObjectAnimationUsingKeyFrames>
                                    </Storyboard>
                                </vsm:VisualState>
                                <vsm:VisualState x:Name=”InvalidFocused”>
                                    <Storyboard>
                                        <ObjectAnimationUsingKeyFrames Storyboard.TargetName=”ValidationErrorElement” Storyboard.TargetProperty=”Visibility”>
                                            <DiscreteObjectKeyFrame KeyTime=”0″>
                                                <DiscreteObjectKeyFrame.Value>
                                                    <Visibility>Visible</Visibility>
                                                </DiscreteObjectKeyFrame.Value>
                                            </DiscreteObjectKeyFrame>
                                        </ObjectAnimationUsingKeyFrames>
                                        <ObjectAnimationUsingKeyFrames Storyboard.TargetName=”validationTooltip” Storyboard.TargetProperty=”IsOpen”>
                                            <DiscreteObjectKeyFrame KeyTime=”0″>
                                                <DiscreteObjectKeyFrame.Value>
                                                    <sys:Boolean>True</sys:Boolean>
                                                </DiscreteObjectKeyFrame.Value>
                                            </DiscreteObjectKeyFrame>
                                        </ObjectAnimationUsingKeyFrames>
                                    </Storyboard>
                                </vsm:VisualState>
                            </vsm:VisualStateGroup>

                        </vsm:VisualStateManager.VisualStateGroups>
                        <Border x:Name=”Border”
                    Opacity=”1″
                    Background=”{TemplateBinding Background}”
                    BorderBrush=”{TemplateBinding BorderBrush}”
                    BorderThickness=”{TemplateBinding BorderThickness}”
                    CornerRadius=”2,2,2,2″>
                            <Grid>
                                <Border x:Name=”ReadOnlyVisualElement”
                        Opacity=”0″
                        Background=”#72F7F7F7″/>
                                <Border BorderThickness=”1″
                        CornerRadius=”1,1,1,1″>
                                    <Border.BorderBrush>
                                        <SolidColorBrush Color=”Transparent”
                                     x:Name=”MouseOverColor”/>
                                    </Border.BorderBrush>
                                    <ScrollViewer BorderThickness=”0″
                                IsTabStop=”False”
                                Padding=”{TemplateBinding Padding}”
                                x:Name=”ContentElement”/>
                                </Border>
                            </Grid>
                        </Border>
                        <Border x:Name=”HoverBorder”
                    Opacity=”0″
                    BorderBrush=”{StaticResource NormalBrush}”
                    BorderThickness=”2,2,2,2″
                    CornerRadius=”2,2,2,2″/>
                        <Border x:Name=”DisabledVisualElement”
                    IsHitTestVisible=”False”
                    Opacity=”0″
                    Background=”#FFFFFFFF”
                    BorderBrush=”#A5F7F7F7″
                    BorderThickness=”{TemplateBinding BorderThickness}”
                    CornerRadius=”2,2,2,2″/>
                        <Border Margin=”1″
                    x:Name=”FocusVisualElement”
                    IsHitTestVisible=”False”
                    Opacity=”0″
                    BorderBrush=”{StaticResource NormalBrush}”
                    BorderThickness=”2.1,2.1,2.1,2.1″
                    CornerRadius=”0.2,0.2,0.2,0.2″/>
                        <Border x:Name=”ValidationErrorElement” BorderThickness=”1″ CornerRadius=”1″ BorderBrush=”#FFDB000C” Visibility=”Collapsed”>
                            <ToolTipService.ToolTip>
                                <ToolTip x:Name=”validationTooltip” Template=”{StaticResource ValidationToolTipTemplate}” Placement=”Right”
                         PlacementTarget=”{Binding RelativeSource={RelativeSource TemplatedParent}}”
                         DataContext=”{Binding RelativeSource={RelativeSource TemplatedParent}}”>
                                    <ToolTip.Triggers>
                                        <EventTrigger RoutedEvent=”Canvas.Loaded”>
                                            <EventTrigger.Actions>
                                                <BeginStoryboard>
                                                    <Storyboard>
                                                        <ObjectAnimationUsingKeyFrames Storyboard.TargetName=”validationTooltip” Storyboard.TargetProperty=”IsHitTestVisible”>
                                                            <DiscreteObjectKeyFrame KeyTime=”0″>
                                                                <DiscreteObjectKeyFrame.Value>
                                                                    <sys:Boolean>true</sys:Boolean>
                                                                </DiscreteObjectKeyFrame.Value>
                                                            </DiscreteObjectKeyFrame>
                                                        </ObjectAnimationUsingKeyFrames>
                                                    </Storyboard>
                                                </BeginStoryboard>
                                            </EventTrigger.Actions>
                                        </EventTrigger>
                                    </ToolTip.Triggers>
                                </ToolTip>
                            </ToolTipService.ToolTip>
                            <Grid Width=”12″ Height=”12″ HorizontalAlignment=”Right” Margin=”1,-4,-4,0″ VerticalAlignment=”Top” Background=”Transparent”>
                                <Path Margin=”1,3,0,0″ Data=”M 1,0 L6,0 A 2,2 90 0 1 8,2 L8,7 z” Fill=”#FFDC000C”/>
                                <Path Margin=”1,3,0,0″ Data=”M 0,0 L2,0 L 8,6 L8,8″ Fill=”#ffffff”/>
                            </Grid>
                        </Border>
                    </Grid>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>