onScroll function can't find RadGrid

[Jeff]

I am trying to follow the example on scrolling (the second grid in the example with yahoo style scrolling) of a RadGrid found here:

http://demos.telerik.com/aspnet-ajax/grid/examples/client/virtualscrollpaging/defaultcs.aspx

but 

var grid = $find("<%=RadGrid2.ClientID %>")


just returns null. Have tried everything I can think of but to no avail. My RadGrid is just sitting inside a div in context of the page. Any thoughts? Thanks!