Warning: require_once(mainfile.php): failed to open stream: No such file or directory in /home/thader/public_html/index.php on line 15

Fatal error: require_once(): Failed opening required 'mainfile.php' (include_path='.:/opt/cpanel/ea-php56/root/usr/share/pear') in /home/thader/public_html/index.php on line 15