PHPBB Bridge Plugin Error

I have started getting an error showing up since I installed the PHPBB Bridge plugin. It is happening on a different part of the website that I use to full the latest 3 posts from wordpress and show them on a php page.

This is the Error;

Warning: Cannot modify header information - headers already sent by (output started at /home/webbysit/public_html/includes/header.php:4) in /home/webbysit/public_html/blog/wp-includes/pluggable.php on line 667

Warning: Cannot modify header information - headers already sent by (output started at /home/webbysit/public_html/includes/header.php:4) in /home/webbysit/public_html/blog/wp-includes/pluggable.php on line 668

Warning: Cannot modify header information - headers already sent by (output started at /home/webbysit/public_html/includes/header.php:4) in /home/webbysit/public_html/blog/wp-includes/pluggable.php on line 669

And this is the php code I use to pull the titles from wordpress;

<ul class="latest_post">
<?php require($_SERVER['DOCUMENT_ROOT'] . '/blog/wp-load.php'); query_posts('showposts=3');  if (have_posts()) : while (have_posts()) : the_post(); ?>
        <li>
          <div class="date"><span>
              <?php the_time('d') ?>
              </span>
              <?php the_time('M') ?>
            </div>
           <a href="<?php the_permalink(); ?>" title="<?php the_title(); ?>">
            <?php the_title(); ?>
            </a>
            <div class="clear"></div>
        </li>
        <?php endwhile; else: echo "no posts"; endif; ?>
        <?php wp_reset_query(); ?>
                    </ul>

I hope somebody can help.

Thanks