ciao ragazzi ... chi mi sa aiutare a fixare questo errore???

Warning: Cannot modify header information - headers already sent by (output started at /home/web/www.sito.net/www/forum/wap/topicop.php:1) in /home/web/www.sito.net/www/forum/wap/wapheader.php on line 11

Warning: Cannot modify header information - headers already sent by (output started at /home/web/www.sito.net/www/forum/wap/topicop.php:1) in /home/web/www.sito.net/www/forum/wap/wapheader.php on line 12

ma in quelle linee ho scritto questo:

header("Content-type: text/vnd.wap.wml");
header("Cache-Control: no-cache, must-revalidate");

come posso risolvere???

grazie a ki mi saprà aiutare....e auguri...