Thank you for contacting us.
If you want using of obsolete events, methods and properties to break your build, you need to turn on Treat Warning As Errors
for your project from Visual Studio.
This event was obsolete, because it was called synchronously right in the middle of the window.Show()
method, which means that you could move your code from the handler of the Opened event just after the call to the Show method.
All the best,
the Telerik team
Register for the Q2 2011 What's New Webinar Week. Mark your calendar for the week starting July 18th and book your seat for a walk through of all the exciting stuff we will ship with the new release!