Achive shows last post instead of category list

Hi,

I use the CleanMag theme, my menu has a few category items.
When I click a category in my menu, the only post that I see is the last post I did in that category, instead of a list of posts in that category…

This is the archive.php code for CleanMag, it seems to be ok. But I think it is a setting or someting else…

Who is the supergenius that can help me out?

<?php get_header(); ?>
<div id="post" class="grid_17 alpha">
	<?php if (have_posts()) : ?>

	<?php $post = $posts[0]; ?>
	<?php if (is_category()) { ?>

	<?php } elseif( is_tag() ) { ?>
	<h3 id="archive-title">Posts met het label &quot;<?php single_tag_title(); ?>&quot;</h3>
	<?php  } elseif (is_day()) { ?>
	<h1 id="archive-title">Archief voor <?php the_time('F jS, Y'); ?></h1>
	<?php  } elseif (is_month()) { ?>
	<h1 id="archive-title">Archief voor <?php the_time('F, Y'); ?></h1>
	<?php  } elseif (is_year()) { ?>
	<h1 id="archive-title">Archief voor <?php the_time('Y'); ?></h1>
	<?php  } elseif (isset($_GET['paged']) && !empty($_GET['paged'])) { ?>

	<?php } ?>

		<?php echo category_description( $category ); ?>
   <!-- END sub-description --> 

    <!-- END entry -->

	<?php get_template_part( 'post' , 'entry') ?>
	<?php if (function_exists("pagination")) { pagination($additional_loop->max_num_pages); } ?>
    <?php endif; ?>
</div>
<!-- END post -->
<?php get_sidebar(' '); ?>
<?php get_footer(' '); ?>