Fixing an error which is not making part of the website work

Our wordpress is showing this error:

Warning: require(/homepages/15/d29451860/htdocs/clickandbuilds/intertektrading/de/wp-includes/post.php): failed to open stream: Permission denied in /homepages/15/d29451860/htdocs/clickandbuilds/intertektrading/de/wp-settings.php on line 166

Fatal error: require(): Failed opening required '/homepages/15/d29451860/htdocs/clickandbuilds/intertektrading/de/wp-includes/post.php' (include_path='.:/usr/lib/php7.0') in /homepages/15/d29451860/htdocs/clickandbuilds/intertektrading/de/wp-settings.php on line 166

Can someone please support us to fix it?