line of php making dynamic sidebar disappear

i installed and have augmented the prosumer theme on my wp. i also installed the phpbb3 plugin to call up the last few topics posted in the forum.

the problem comes when i edit the index file to add:

<div class="gap">
    <?php phpbb_recent_posts(); ?>
</div>

it disables every php tag that comes after it, which would be:

<?php get_sidebar(); ?>
<?php get_footer(); ?>

i really have no clue what’s causing this or why a string of self-ending php would cause anything following it not to work