Why this db_query used in Drupal 7 Rules custom PHP crashes my website

Question

I can execute this code in a page node like a PHP code, but when I try to run on a custom php action in Drupal 7 Rules, my website crashes (white screen). What's wrong?

$OrderID_miquel="40";
$query = db_query('Select MAX(field_delivery_package_numerical_value) AS MaxDelivery , order_id , nid FROM {field_data_field_delivery_package_numerical} , {uc_order_products} WHERE order_id = :order_id' , array( ':order_id' => $OrderID_miquel));