I was using a debug build of our 3.0.1.0. That method is exposed in the debug build but not in the release build. I will have to discuss why this was done with Stefan, the grid architect. There must be another way to get at this information that I am not seeing.
Anyway, for now, to get that code working in release, you can add this method to the form class,
public int GetRowIndex(Element el)
{
return this.gridGroupingControl1.Engine.Table.NestedDisplayElements.IndexOf(el);
}
Then replace the offending line with this line:
int offset = GetRowIndex((GridRecord)gnt.ChildTable.GetFirstRecord())- GetRowIndex(gnt.ChildTable);