Not clear what you were trying to do here
.Cells(rs.RecordCount + 5, iCol + 1).Value= "=Sum("Colsum" & iCol)"
since code is not complete it is hard to tell, as forexample what is colsum etc
i would guess you would need to change some thing close to
.Cells(rs.RecordCount + 5, iCol + 1).formula= "=Sum(" & Colsum & iCol & ")"