Royco

hi all, im doing a login.php page that analyses the user and password of a previous html form. For this login to analyse the user/pass, it must connect to a database and use a "require_once" and a "include" in its code. when i run this login on my computer, it works fine. But when i use it on the online server, i get the: " Warning: Cannot modify header information - headers already sent by (output started at /home/rodrigopitta/www/teste/main.php:17) in /home/rodrigopitta/www/teste/login.php on line 21 " main.php is the file that is "required_once" i also have removed any blank spaces before the <?php and after the ?>.... must i delete the require_once or include files and make a direct connection to the database on every php page that requires a "header("Location: $header_login");" ? what is the best way to redirect a page once the user/pass returns true? should i continue to use the headers method? thanks everyone.