Hi Sathya Prasaad,
Thank your for contacting us.
Telerik.Windows.Quickstart.Dialogs appears for the first time in the Beta for Q1 2010 which was released on 02.18.2010.
We apologize but we don't support controls in this (Telerik.Windows.Quickstart.Dialogs) assembly, we used them only in our online telerik demos. You can find all our controls we support here.
the Telerik team
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