<p><?php printf(__('You must be <a href="%s">logged in</a> to post a comment.'), wp_login_url( get_permalink() )); ?></p>
<?php else : ?>
-<form action="<?php echo get_option('siteurl'); ?>/wp-comments-post.php" method="post" id="commentform">
+<form action="<?php echo site_url(); ?>/wp-comments-post.php" method="post" id="commentform">
<?php if ( is_user_logged_in() ) : ?>