The application you sent works as I expected. Pressing the button opens the popup.
The problem you're reporting might be connected to a popup blocker implemented by your browser (or some browser add-on, such as google toolbar).
Try to disable all popup blockers, and reload your application.
If the problem persists, you can try replacing Display/Popup with Display/Dialog which is similar, except the former is implemented using a separate browser window (and thereby susceptible to popup blockers), whereas the latter is implemented as a layer in the same browser window as the view launching it.
For best results, use the Firefox browser..