failed to open stream wp-settings.php on line 21

Warning: require() [function.require]: Unable to access /home/perfec75/public_html/theadvancednetwork.co.uk/wp-includes/load.php in /home/perfec75/public_html/theadvancednetwork.co.uk/wp-settings.php on line 21

Warning: require(/home/perfec75/public_html/theadvancednetwork.co.uk/wp-includes/load.php) [function.require]: failed to open stream: Permission denied in /home/perfec75/public_html/theadvancednetwork.co.uk/wp-settings.php on line 21

Warning: require() [function.require]: Unable to access /home/perfec75/public_html/theadvancednetwork.co.uk/wp-includes/load.php in /home/perfec75/public_html/theadvancednetwork.co.uk/wp-settings.php on line 21

Warning: require(/home/perfec75/public_html/theadvancednetwork.co.uk/wp-includes/load.php) [function.require]: failed to open stream: Permission denied in /home/perfec75/public_html/theadvancednetwork.co.uk/wp-settings.php on line 21

Fatal error: require() [function.require]: Failed opening required ‘/home/perfec75/public_html/theadvancednetwork.co.uk/wp-includes/load.php’ (include_path=’.:/usr/lib/php:/usr/local/lib/php’) in /home/perfec75/public_html/theadvancednetwork.co.uk/wp-settings.php on line 21

Website has crashed and getting this error now, and cannot login into wordpress and use the dashboard. Does anyone have any suggestions on how to solve this problem? This is the second time it’s happened, and last time I deleted the entire site and rebuilt. There must be a quicker method. Does anyone know what it causing this?

Thanks very much