Can't see comments on posts

Hi there,

I have a problem with being able to view comments. All that is shown is e.g. ‘2 responses to {post title]’
Please see here: http://preview.screencult.com/services/viral-videos/when-does-a-film-become-a-cult-film/

For some reason it shows the admin response but not the response of the other user. Why is this? I have checked the comments.php and single.php, as well the original TwentyTen theme ones to see the difference but there are none.

At the moment the code for the comments.php looks like this:

<?php
	// You can start editing here -- including this comment!
?>

<?php if ( have_comments() ) : ?>
			<h3 id="comments-title"><?php
			printf( _n( 'One Response to %2$s', '%1$s Responses to %2$s', get_comments_number(), 'twentyten' ),
			number_format_i18n( get_comments_number() ), '<em>' . get_the_title() . '</em>' );
			?></h3>

<?php if ( get_comment_pages_count() > 1 && get_option( 'page_comments' ) ) : // Are there comments to navigate through? ?>
			<div class="navigation">
				<div class="nav-previous"><?php previous_comments_link( __( '<span class="meta-nav">&larr;</span> Older Comments', 'twentyten' ) ); ?></div>
				<div class="nav-next"><?php next_comments_link( __( 'Newer Comments <span class="meta-nav">&rarr;</span>', 'twentyten' ) ); ?></div>
			</div> <!-- .navigation -->
<?php endif; // check for comment navigation ?>

			<ol class="commentlist">
				<?php
					/* Loop through and list the comments. Tell wp_list_comments()
					 * to use twentyten_comment() to format the comments.
					 * If you want to overload this in a child theme then you can
					 * define twentyten_comment() and that will be used instead.
					 * See twentyten_comment() in twentyten/functions.php for more.
					 */
					wp_list_comments( array( 'callback' => 'twentyten_comment' ) );
				?>
			</ol>

<?php if ( get_comment_pages_count() > 1 && get_option( 'page_comments' ) ) : // Are there comments to navigate through? ?>
			<div class="navigation">
				<div class="nav-previous"><?php previous_comments_link( __( '<span class="meta-nav">&larr;</span> Older Comments', 'twentyten' ) ); ?></div>
				<div class="nav-next"><?php next_comments_link( __( 'Newer Comments <span class="meta-nav">&rarr;</span>', 'twentyten' ) ); ?></div>
			</div><!-- .navigation -->
<?php endif; // check for comment navigation ?>

<?php else : // or, if we don't have comments:

	/* If there are no comments and comments are closed,
	 * let's leave a little note, shall we?
	 */
	if ( ! comments_open() ) :
?>
	<p class="nocomments"><?php _e( 'Comments are closed.', 'twentyten' ); ?></p>
<?php endif; // end ! comments_open() ?>

<?php endif; // end have_comments() ?>

<?php comment_form(); ?>

</div><!-- #comments -->

Also my single.php has <?php comments_template( '', true ); ?>

Any reasons for the problem? Could it be a plug-in overriding it?