Advarsel:mysql_num_rows():det angivne argument er ikke en gyldig MySQL-resultatressource

Skift $result = @mysql_query ($query);

med

$result = mysql_query ($query) or die(mysql_error());

og se om du har nogle fejl.

EDIT:

Du gik glip af et komma efter oc.price og før prd.products_id. Skift din forespørgsel sådan her:

$query = "SELECT us.users_id, us.users_first_name, us.users_surname, us.users_business, 
             ord.order_id, ord.users_id, ord.total, ord.order_date,  
             oc.oc_id, oc.order_id, oc.products_id, oc.quantity, oc.price/*here*/,/**/
             prd.products_id, prd.products_name, prd.price      
         FROM users AS us, orders AS ord, order_contents AS oc, products AS prd  
         WHERE ord.order_id=$id
         AND us.users_id = ord.users_id
         AND ord.order_id = oc.order_id
         AND oc.products_id = prd.products_id    
         ";