Well I’ve found the problem causing this error (which was occuring inside the archive list as well)
<div class="left-nav">
<h2>Other posts</h2>
<?php
$posts=get_posts('numberposts=5');
foreach ($posts as $post) :
?>
<?PHP the_time("d.m.y"); ?><a href="<?PHP the_permalink(); ?>"><?PHP the_title(); ?></a>
<?PHP endforeach; ?>
</div>
This was made to display 5 posts.
Is there an easier way I should know of?