Using this code: 

<?php
exec("online.bat param1");
header("Location:http://myserver/mypage.php");
exit;
?>

my browsers (IE and Mozilla) instead of do a redirect they display this message:

Status: 302
Content-type: text/html
X-Powered-By: PHP/4.3.1
Location:http://myserver/mypage.php

That is the full "dump" of the HTTP header of a Redirect (302) but it seems that exec() put into output stream any char that causes browsers to misunderstand the header and consider it an "raw text output".

Commenting exec or calling other function makes the script working correctly and the browser works ok.

Best regards.

P.S.: PHP is working as CGI on Netscape iPlanet Web Server.