Assigning a Style in custom WP renderers

I've created a custom render for my switches in WP, in this render I assign a style I've defined in the App.xaml

<Style x:Key="ToggleSwitchWithMargin" TargetType="controls:ToggleSwitch">
            <Setter Property="Background" Value="{StaticResource PhoneBackgroundBrush}"/>
            <Setter Property="FontFamily" Value="{StaticResource PhoneFontFamilyLight}"/>
            <Setter Property="FontSize" Value="{StaticResource PhoneFontSizeLarge}"/>
            <Setter Property="Foreground" Value="{StaticResource PhoneForegroundBrush}"/>
            <Setter Property="IsTabStop" Value="False"/>
            <Setter Property="HorizontalContentAlignment" Value="Left"/>
            <Setter Property="SwitchForeground" Value="{StaticResource PhoneAccentBrush}"/>
            <Setter Property="VerticalContentAlignment" Value="Top"/>
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="controls:ToggleSwitch">
                        <Border BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" CacheMode="BitmapCache" Padding="{TemplateBinding Padding}">
                            <VisualStateManager.VisualStateGroups>
                                <VisualStateGroup x:Name="CommonStates">
                                    <VisualState x:Name="Normal"/>
                                    <VisualState x:Name="Disabled">
                                        <Storyboard>
                                            <DoubleAnimation Duration="0" To="0.3" Storyboard.TargetProperty="Opacity" Storyboard.TargetName="Header"/>
                                            <DoubleAnimation Duration="0" To="0.3" Storyboard.TargetProperty="Opacity" Storyboard.TargetName="Content"/>
                                        </Storyboard>
                                    </VisualState>
                                </VisualStateGroup>
                            </VisualStateManager.VisualStateGroups>
                            <Grid Margin="12,5,12,0">
                                <Grid.ColumnDefinitions>
                                    <ColumnDefinition Width="*"/>
                                    <ColumnDefinition Width="Auto"/>
                                </Grid.ColumnDefinitions>
                                <Grid.RowDefinitions>
                                    <RowDefinition Height="Auto"/>
                                    <RowDefinition Height="Auto"/>
                                </Grid.RowDefinitions>
                                <ContentControl x:Name="Header" ContentTemplate="{TemplateBinding HeaderTemplate}" Content="{TemplateBinding Header}" Foreground="{StaticResource PhoneSubtleBrush}" FontSize="{StaticResource PhoneFontSizeNormal}" FontFamily="{StaticResource PhoneFontFamilyNormal}" HorizontalAlignment="Left" IsTabStop="False" Margin="-1,0,0,0" Opacity="{TemplateBinding Opacity}" VerticalAlignment="Bottom"/>
                                <ContentControl x:Name="Content" ContentTemplate="{TemplateBinding ContentTemplate}" Content="{TemplateBinding Content}" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" IsTabStop="False" Margin="-1,1,0,-7" Opacity="{TemplateBinding Opacity}" Grid.Row="1" VerticalAlignment="{TemplateBinding VerticalContentAlignment}"/>
                                <toolkitPrimitives:ToggleSwitchButton x:Name="Switch" Background="{TemplateBinding Background}" Grid.Column="1" Margin="-22,-29,-24,-28" Opacity="{TemplateBinding Opacity}" Grid.RowSpan="2" SwitchForeground="{TemplateBinding SwitchForeground}" VerticalAlignment="Bottom"/>
                            </Grid>
                        </Border>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>

To assign this style i use the following code:

var style = App.Current.Resources["ToggleSwitchWithMargin"] as System.Windows.Style;
Control.Style = style;

But once the render runs i get the following exception______
Catastrophic failure (Exception from HRESULT: 0x8000FFFF (E_UNEXPECTED))

Is this the work way to assign styles?