Vista - ListBox, Style & ContextMenu

Hi,

I have a problem. I am new to WPF and I thought I could set a ContextMenu
for my ListBox via a Style so I wrote sth like this:

<Window x:Class="TestTheTestStudio.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Window1" Height="300" Width="300" Loaded="Window_Loaded">
<Window.Resources>
<Style TargetType="{x:Type ListBox}">
<Setter Property="ContextMenu">
<Setter.Value>
<ContextMenu Name="test">
<MenuItem Header="Test"/>
</ContextMenu>
</Setter.Value>
</Setter>
</Style>
</Window.Resources>
<StackPanel>
<Button x:Name="buttonTest" Click="buttonTest_Click">Add</Button>
<ListBox>
<ListBox.Items>
<ListBoxItem>Test</ListBoxItem>
</ListBox.Items>
</ListBox>
</StackPanel>
</Window>

My code compiles. But after that I get a Exception from the XamlReader
saying that
a object of type "System.Object" must not have content of type
"System.Windows.Controls.ContextMenu". I do not understand what I am doing
wrong...maybe it is sth very simple.

Thanks, Pan