IE WebControls TreeView - javascript issue in web app

I am using the old Microsoft.Web.UI.WebControls TreeView control. When running under a web application, a method treeview.GetChildren()

via object or proprieta is not supported error, but the same code in the asp.net 2.0 site project works fine.

Has anyone encountered this problem? There is almost nothing about this in this control ...

thanks for any help.