note 42341 added to function.header

I used the function header() in order to force a download. This worked well for a couple of times but then I got the error: "can't add header ...; they are already sent" But I use the header function at the beginning of my php file. The header_sent() function returns TRUE but I can't use the overloaded function to find out where the headers are sent. Can anybody help me? ---- Manual Page -- http://www.php.net/manual/en/function.header.php Edit -- http://master.php.net/manage/user-notes.php?action=edit+42341 Delete -- http://master.php.net/manage/user-notes.php?action=delete+42341&report=yes Reject -- http://master.php.net/manage/user-notes.php?action=reject+42341&report=yes Search -- http://master.php.net/manage/user-notes.php