Header already.... when header() is used...PHP

When I use header( 'Location: http://www.yoursite.c开发者_如何学运维om/new_page.html' ) ; which is a PHP redirection of page, it says header already passed at line....

The landing page as <? include('header.php'); ?>

How can I over come this error message?

Appreciate assistance.

Thanks Jean

---

Note that headers should be sent before anything else. Make sure that there is no code/html or even space/indentation before the header function and there is nothing before the first opening php tag <?php as well as ending tag ?> in your page.