Code in header.php gives syntax error

Dear all,

For my site http://www.kavel10.nl I want to have a clean homepage, without a menu on it. I researched the forum and saw that the most straightforward option to do this was to insert the following code into the header.php file of my theme (I use Advantage).

<?php if ( !is_front_page() ): ?>

<nav id="access" role="navigation">
<?php wp_nav_menu( array( 'theme_location' => 'header_nav', 'container_id' => 'header-nav', 'container_class' => 'nav', 'fallback_cb' => 'minimatica_nav_menu' ) ); ?>
</nav><!-- #access -->

<?php endif; ?>

From this post: http://ww.wp.xz.cn/support/topic/how-do-i-remove-header-menu-from-home-page-only-1?replies=7

However, when I paste this behind the rest of the code that’s already there, my site displays a syntax error, it says ‘on line 39’. I don’t know why this happens, or how to solve this. It shouldn’t matter if I place it at the end of the code, should it? Any leads?

Thank you very much!

Sophie