(copied from: source)
====================
1) there should not be any output (i.e. echo..
or HTML codes) before the header(.......);
command.
2) remove any white-space(or newline) before <?php
and after ?>
tags.
3) GOLDEN RULE! - check if that php file (and also, if you include
other files) have UTF8 without BOM encoding (and not just UTF-8). That is problem in many cases (because UTF8 encoded file has something special character in the start of php file, which your text-editor doesnt show)!!!!!!!!!!!
4) After header(...);
you must use exit;
5) always use 301 or 302 reference:
header("location: http://example.com", true, 301 ); exit;
6) Turn on error reporting, and find the error. Your error may be caused by a function that is not working. When you turn on error reporting, you should always fix top-most error first. For example, it might be "Warning: date_default_timezone_get(): It is not safe to rely on the system's timezone settings." - then farther on down you may see "headers not sent" error. After fixing top-most (1st) error, re-load your page. If you still have errors, then again fix the top-most error.
7) If none of above helps, use JAVSCRIPT redirection(however, strongly non-recommended method), may be the last chance in custom cases...:
echo "<script type='text/javascript'>window.top.location='http://website.com/';</script>"; exit;