Yo tambien creo que el problema anda en ese archivo por descarte...
Te lo pego, creo que demomento no he modificado nada d este archivo.
Código PHP:
<?php get_header(); ?>
<div id="content">
<?php if (have_posts()) : while (have_posts()) : the_post(); ?>
<div class="post" id="post-<?php the_ID(); ?>">
<h2><?php the_title(); ?></h2>
<div class="top-tools">Posted By <span><?php the_author() ?></span> on <span><?php the_time('F jS, Y') ?></span> <?php edit_post_link('Edit', '', ' '); ?></div>
<div class="entry">
<?php if ( get_post_meta($post->ID, 'thumbnail', true) ) { ?> <br class="clear-fix"/>
<div class="post-thumbnail"><img src="<?php $key="thumbnail"; echo get_post_meta($post->ID, $key, true); ?>" alt="<?php the_permalink() ?>"/></div>
<?php } ?>
<?php the_content('<p class="serif">Read the rest of this entry »</p>'); ?>
<?php wp_link_pages(array('before' => '<p><strong>Pages:</strong> ', 'after' => '</p>', 'next_or_number' => 'number')); ?>
<?php the_tags( '<p>Tags: ', ', ', '</p>'); ?>
<div class="tools no-border"><div class="float-left"><span>Similar Posts</span> </div><div class="float-right share"><span>Share</span></div></div>
<ul class="list-items share">
<li><a href="http://digg.com/submit?phase=2&url=<?php the_permalink() ?>&title=<?php the_title(); ?>" title="Digg this story" rel="nofollow">Digg</a></li>
<li><a href="http://www.stumbleupon.com/submit?url=<?php the_permalink(); ?>&title=<?php the_title(); ?>" rel="nofollow"> Stumble it!</a> </li>
<li><a href="http://reddit.com/submit?url=<?php the_permalink(); ?>&title=<?php the_title(); ?>" rel="nofollow">Reddit</a></li>
</ul>
<ul class="list-items">
<?php
related_posts_by_category(
array(
'orderby' => 'post_date',
'order' => 'DESC',
'limit' => 3,
'echo' => true,
'before' => '<li>',
'after' => '</li>',
'rel' => 'nofollow',
'type' => 'post',
'message' => '<li><a href=#">no related posts</a></li>'
)
);
?>
</ul>
<div class="tools"><div class="float-left"><span>Posted in</span> <?php the_category(', ') ?> </div><div class="float-right share"><span><?php comments_number('Comments 0', 'Comments 1', 'Comments %' );?></span></div></div>
</div>
</div>
<?php comments_template(); ?>
<?php endwhile; else: ?>
<p>Sorry, no posts matched your criteria.</p>
<?php endif; ?>
</div>
<?php get_sidebar(); ?>
<?php get_footer(); ?>