well I cant tell you why but this line calls the
vb directory
require_once(DIR . '/includes/functions_wysiwyg.php');
I would assume its suppose to read
/usr/www/users/blauev/includes/functions_wysiwyg.php
your error is becauses yours reads this
/usr/www/users/blauevhttp://www.domain.com/includes/functions_wysiwyg.php
what exactly is the proper server path you see what I mean
If you have any plugins try disabling them and then see if you get the error because no one reports an error like this.