How to display or hide the Group Tree in CrystalReportViewer


I'm a newbie wrt to Dotnet, I have .NET 3.5 framework and I have done a ASP .NET project with Visual studio 2008 with crystal reports 2008. I get 'DisplayGroupTree' property cannot be set declaratively error when I try to build my project.

Could someone explain me in detail how to achieve what is mentioned in this link?