Ooopss... my bad.
i meant no white spaces before the opening <?php tag that contains the call to header() function..
not white space after the closing ?> tag...
let me rephrase that ...
if you are putting header in php tag:
<?php
header ("Location: http://mysite/hi.php");
?>
make sure that if you include anything before you get to the header part (be it from require_once(), include_once(), print, or whatever else), make sure that you don't have white spaces lying around your source code.
otherwise, the blank space will be sent to the browser, and after that no header() can be sent to the browser, resulting in header already sent error.
after the header, it won't matter if you put tens of thousands of millions of white spaces .. they won't affect the header()s
sorry for the confusion ... ><;;
[ disoriented morning ]