well it was more to do with this reference
$_GET['OptionGroupID'] = $row_ProductDetail["ProductID"];
as this is getting the ID from another recordset on the page and is the reason I am trying to convert as the other rs is mysqli
what I am trying to do is convert product options that we worked on on one site (attached detail-products.php) which uses mysql to mysqli on another site (attached product_s.php). The db structure is exactly the same on both