I was customizing the Category Archive template when I had an issue - there was an extra </div> somewhere, messing up the page. A bit of digging revealed it was in the loop.php on line 171.
<?php /* Display navigation to next/previous pages when applicable */ ?> <?php if ( $wp_query->max_num_pages > 1 ) : ?> <nav id="nav-below" class="navigation"> <div class="nav-previous"><?php next_posts_link( __( '← Older posts', 'boilerplate' ) ); ?></div> <div class="nav-next"><?php previous_posts_link( __( 'Newer posts →', 'boilerplate' ) ); ?></div> </div><!-- #nav-below --> <?php endif; ?>
See where it says
<!-- #nav-below -->? That should be
</nav>. Thought you should know.