Header Error Message

Hi All,

The site is question is the hompage https://www.rockyformayor.com if you take a look at the footer you can see that I have called in the 3 most recent posts from the blog page.

Every now and then I get the following error.
Warning: Cannot modify header information – headers already sent by (output started at /home/rockyfor/public_html/index.php:8) in /home/rockyfor/public_html/blog/wp-content/plugins/wp-super-cache/wp-cache-phase2.php on line 71

Here is the code I’m using to call in the posts.

<?php require('./blog/wp-blog-header.php');?>
    <ul>
	<?php query_posts('showposts=3'); ?>
	<?php while (have_posts()) : the_post(); ?>
	<li><a href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title(); ?>"><?php the_title(); ?></a></li><br />
	<?php endwhile;?>
    </ul>

Any help is appreciated sometimes the messages comes up and sometimes it does not.