im developing a wordpress blog and im getting the next warning that keeps approaching,

Warning: Cannot modify header information - headers already sent by (output began at /home/content/66/7511066/html/zen/wordpress-content/styles/ZenOfficePortfolio/functions.php:20) in /home/content/66/7511066/html/zen/wordpress-includes/pluggable.php online 934

after i attempted this code in your area on my small machine, it labored fine. however, if i moved the code to the hosting website, i keep obtaining the error

my functions.php is the following

<?php
    if(function_exists('register_sidebar')){
        register_sidebar(array('name' => 'ZenOffice'));
    } 

        add_filter('comments_template', 'legacy_comments');
    function legacy_comments($file) {
        if ( !function_exists('wp_list_comments') ) 
            $file = TEMPLATEPATH . '/old-comments.php';
        return $file;
    }

    //Set the theme categories
    define('BLOG',15);
    define('PORTFOLIO',14);
?>

I believe iv solved it,

i simply ensured there have been no whitened spaces as @Pekka recommended. after which i re submitted the file.

appears to become working now.