comments 404 error – never ending story

Hello!

I′ve tried everything. I search for a couple of days now and have tried any written tip founded but nothing solve my problem. So I hope to find a wordpress expert here who knows the answer …

The Problem:
When I add a comment a 404 error is the result. The URL after clicking the “submit” button is wrong:

https://hoffmann-bauunternehmen.de/http%3A%2F%2Fhoffmann-bauunternehmen.de%2Fgaestebuch%2F#comment-48

If you want to trie the comments function use this site please:

guestbook

When I activate the standard theme comments works correctly. The theme author is no real help, so I hope to get a working solution here. The theme I use is the commercial horizon theme, to find here:

https://horizon.webtemplatemasters.com/

The comments.php looks like this:

<?php
	if (!empty($_SERVER['SCRIPT_FILENAME']) && 'comments.php' == basename($_SERVER['SCRIPT_FILENAME']))
		die ('Please do not load this page directly.');

	if ( post_password_required() ) { ?>
		<h4 class="nocomments"><?php _e('This post is password protected. Enter the password to view comments.', 'horizon') ?></h4>
	<?php
		return;
	}

//Comments List

	 if ( have_comments() ) : // if there are comments ?>
	 <!-- post comments -->
    <div class="comment-list" id="comments">
		<h4><?php comments_number( '0 '.__('Comments','horizon'), '1 '.__('Comment','horizon'), '% '.__('Comments','horizon')); ?></h4> 

<ol>
		<?php wp_list_comments('avatar_size=100&callback=tmk_comment'); ?>
		</ol>
	</div><!--/ #comments-->
 <!--/ post comments -->
 <?php

//Comments error messages

		if ('closed' == $post->comment_status ) : // if the post has comments but comments are now closed ?>

		<?php endif; ?>

 		<?php else :  ?>

        <?php if ('open' == $post->comment_status) : // if comments are open but no comments so far ?>

        <?php else : ?>

        <?php endif; ?>

<?php endif;

//Contact Form

	if ( comments_open() ) : ?>
	<!-- add comment -->
	<div class="add-comment" id="addcomments">
		<h4><?php _e('Leave a Reply','horizon'); ?></h4>
		<div class="comment-form">
			<?php if ( get_option('comment_registration') && !is_user_logged_in() ) : ?>
			<?php printf('<p>'.__('You must be %1$slogged in%2$s to post a comment.', 'horizon').'</p>', '<a href="'.get_option('siteurl').'/wp-login.php?redirect_to='.urlencode(get_permalink()).'">', '</a>') ?>
			<?php else: ?>
			<form action="<?php echo get_option('siteurl'); ?>/wp-comments-post.php" method="post" id="commentform">
				<?php if ( is_user_logged_in() ) : ?>
				<p><?php printf(__('Logged in as %1$s. %2$sLog out ?%3$s', 'horizon'), '<a href="'.get_option('siteurl').'/wp-admin/profile.php">'.$user_identity.'</a>', '<a href="get_option('siteurl').'/wp-login.php?action=logout" title="').'">', '</a>') ?></p>
				<?php else : ?>
				<div class="row">
					<input type="text" name="author" id="author" value="" class="inputtext required" />
					<label><?php _e('Your Name','horizon'); ?>: <span>(<?php _e('required','horizon'); ?>)</span></label>
				</div>
				<div class="row">
					<input type="text" name="email" id="email" value="" class="inputtext required" />
					<label><?php _e('E-mail','horizon'); ?>: <span>(<?php _e('will not be published','horizon'); ?>)</span> <span>(<?php _e('required','horizon'); ?>)</span></label>
				</div>
				<div class="row">
					<input type="text" name="url" id="url" value="" class="inputtext required" />
					<label><?php _e('Website','horizon'); ?></label>
				</div>
				<?php endif; ?>
				<div class="row">
					<textarea cols="30" rows="10" name="comment" id="comment" class="textarea textarea_middle required"></textarea>
				</div>
				<input type="hidden" value="<?php echo urlencode(get_permalink()); ?>" name="redirect_to" id="redirect_to" />
				<div class="row">
					<input type="submit" value="Submit" class="button default small" />
				</div>
				<?php comment_id_fields(); ?>
				<?php do_action('comment_form', $post->ID); ?>
			</form>
			<?php endif; ?>
		</div><!--/ comment-form-->
	</div><!--/ addcomments-->
	<!--/add comment -->
	<?php endif; ?>

Thanks!

Martin