Adding a label at the top of the window

Feb 27, 2014 at 1:44 PM
I'm trying to add a label to display error message at the top of the windows just here

Image

Can't find how to do it with the editor..

I tried to add this but it doesn't seems to be the good way...
<Label Content="My Error message" Name="Label_Message" HorizontalAlignment="Left" Margin="267,0,0,0" Width="300" VerticalAlignment="Top" />

Thanks for your help