Vista - Any idea why this is not working?

I want my border to be set to white when the mouseover event is fired any
idea why this is not working?

<Window
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xml:lang="en-US"
x:Class="UntitledProject1.Window1"
x:Name="Window"
Title="Window"
Width="640" Height="480" Background="#FF040404">

<Window.Resources>
<Style TargetType="{x:Type Border}" x:Key="BorderStyle1">
<Style.Triggers>
<Trigger Property="IsMouseOver" Value="True">
<Setter Property="BorderBrush" Value="White"/>
</Trigger>
</Style.Triggers>
</Style>
</Window.Resources>

<Grid x:Name="LayoutRoot">
<Border Margin="103,58,40,88" Style="{DynamicResource BorderStyle1}"
BorderThickness="52,65,58,44" CornerRadius="5,5,5,5"
BorderBrush="#FFD44A4A"/>
</Grid>
</Window>