It seems the Cell and Row Validating events only work when editing an existing cell.
They do not work when adding a new row. The event is called, but the validating code does not work correctly.
Code is fine when updating an existing row.
I can do data validation in the userAddingRow event, but then the ((GridViewDataRowInfo)e.Row).ErrorText = "All Columns Require Data"; produces an error so then you need to use a messagebox.