"System.Windows.Data Error: 4 : Cannot find source for binding with reference 'RelativeSource FindAncestor, AncestorType='Telerik.Windows.Controls.RadWindow', AncestorLevel='1''. BindingExpression:Path=WindowState; DataItem=null; target element is 'RadButton' (Name='PART_CloseButton'); target property is 'NoTarget' (type 'Object')" This error is reported in the Output on startup of a dialog.