Wp_nav_menu not showing on one post page

I am using the Twentytwelve theme and everything is fine, but the navigation menu does not appear on one page of the post, whereas the navigation menu appears on every other page. This is the snippet I am using in header.php to display the menu.

    wp_nav_menu( array(  
       'theme_location'  => 'primary', 
       'menu_class'      => 'nav-menu',
       'container_class' => '',
       'container'       => false,
       'fallback_cb'     => false  ) 
    );