I am using RadDiagram from v. 2012.3.1129 (2012 Q3 SP1) RadControls for SilverLight. but there is no RadDiagramPrintPreview Class in Telerik.Windows.Controls.Diagrams.Extensions Assembly. as mentioned in RadControls For SilverLight Extensions this class should be placed in Telerik.Windows.Controls.Diagrams.Extensions Assembly.