Vista - Media Player Error in XAML Pad

This line in XAML Pad

<Page xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" >
<Grid>
<MediaElement Margin="202,147,241,196" x:Name="MediaElement"
RenderTransformOrigin="0.5,0.5" Source="C:\OldComputer\whymacssuck.wmv"
LoadedBehavior="Play"/>
</Grid>
</Page>

Causes the following error.
No operations are valid on a closed media player except open and close.

Anybody have any ideas on what I am doing wrong.