I saw the video demo. I have created a simple SL app that uses the RadHtmlPlaceholder. I am running this application in OOB. As soon as I click record from Test Studio, my application opens and gives the following message:
"An error has occurred in the script on this page. Unhandled Error in Silverlight Application The invocation of the constructor on type 'Telerik.Windows.Controls.RadHtmlPlaceholder' that matches the specified binding constraints threw an exception. [Line: 16 Position: 46] at System.Windows.Application.LoadComponent(Object component, Uri resourceLocator).."
Here is the xaml code: