Advanced poll works good except for 1 problem?

Hello.
I used Fantastico to intall the advanced poll and it's fully functional except after you click vote and the page refreshes this message comes up at the top of the page "Warning: Cannot modify header information - headers already sent by (output started at /public_html/index.php:3) in /public_html/pollsurvey/poll_cookie.php on line 21" The results of the vote are still shown and it works fine except for that warning message. The message is above everything lik where this is "<?php
// Important! You have to include it before your html code
include_once "/home2/holdem/public_html/pollsurvey/poll_cookie.php";
?>". I would appreciate any help.
Thank you.

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cannot AND modify AND headers

This has been answered numerous times. It's about white space in your files that needs cleaning up.