Hello Katy,
When I customized the layout by placing a control, if the controls are form ESRI or Mircrosoft libraries, I can see the added control in the customized layout in the viewer. just like the "Control in Layout" sample in the Interactive SDK.
However, when I placed a usercontrol created by myself to the customized layout, I could't see anything in viewer(the viewer is blank) after I changed the layout to the customized layout. I can see the control in the customized layout.xaml in design view.
What I am trying to do is to customize the layout by adding a usercontrol which can comunicate with the map.
Your help would be really appreciated
David