Hi Lily,

Thanks for your reply - happily I've now got past the exception in RenderControl.

I've been working from the Hierarchical_Unbound_Programmatic tutorial, and a straight run through works fine.  The problem arises when I try to integrate into our project environment, building the control on demand and picking up the data structure and data from our data objects - it was hard to tell what was causing the crash in RenderControl.  It turns out that I was giving more values in the data array (table.Rows.AddRange) than there were columns in the table; once the right number of values are provided, I get through RenderControl OK. 

Regards,

Robert