Hi, I have found a little bug in line 311 of menupages.inc.php. It seems you are trying to check wp-config.php permissions but in my server (it has ISPCONFIG3 control panel) there is some problem with open_basedir php rule. Maybe you can write the testing condition in a safer way to avoid this warning.
Warning: file_exists() [function.file-exists]: open_basedir restriction in effect. File(/var/www/clients/client1/web1/wp-config.php) is not within the allowed path(s): (/var/www/clients/client1/web1/web:/var/www/clients/client1/web1/tmp:/var/www/mysite.org/web:/srv/www/mysite.org/web:/usr/share/php5:/tmp:/usr/share/phpmyadmin:/etc/phpmyadmin:/var/lib/phpmyadmin) in /var/www/clients/client1/web1/web/wp-content/plugins/quick-cache/includes/classes/menu-pages.inc.php on line 311
Thank you very much