[Plugin: Yet Another Related Posts Plugin] have_posts() fatal error

I had installing YARPP on my site and adding the template code to my single.php file and getting this error when viewing the single post page

Fatal error: Call to a member function have_posts() on a non-object in

the code i had put is …

<?php if ($related_query->have_posts()):?>

<?php while ($related_query->have_posts()) : $related_query->the_post(); ?>
1. ” rel=”bookmark”><?php the_title(); ?>

<?php endwhile; ?>

<?php else: ?>
<p>No related posts.</p>
<?php endif; ?>

please any help ??