note 21105 added to function.session-start

When i create session with session_start() and then run this .php, in the browser show this trouble: - Warning: Cannot send session cookie - headers already sent by (output started at c:\archivos de programa\apache group\apache\htdocs\afieco\usuarios\autentifica.php:4) in c:\archivos de programa\apache group\apache\htdocs\afieco\usuarios\autentifica.php on line 102. However, the web page run well, without problems. I don't know. Why????? Thanks -- http://www.php.net/manual/en/function.session-start.php http://master.php.net/manage/user-notes.php?action=edit+21105 http://master.php.net/manage/user-notes.php?action=delete+21105 http://master.php.net/manage/user-notes.php?action=reject+21105