Plesk UI shows error: PHP Warning: require_once: failed to open stream: No such file or directory

Symptoms

• The following error is shown on Plesk Home page or can be found in /var/www/vhosts/system/example.com/logs/error_log:

  PLESK_ERROR: Error: PHP Warning: require_once(/var/www/vhosts/system/example.com/httpdocs/wp-includes/widgets/class-wp-widget-media.php): failed to open stream: No such file or directory in /var/www/vhosts/system/example.com/httpdocs/wp-includes/default-widgets.php on line 23
  
  PHP Fatal error: require_once(): Failed opening required '/var/www/vhosts/system/example.com/httpdocs/wp-includes/widgets/class-wp-widget-media.php' (include_path='.;.\includes;.\pear') in /var/www/vhosts/system/example.com/httpdocs/wp-includes/default-widgets.php on line 23

• The following can be found at domain log /var/www/vhosts/example.com/logs/proxy_error_log:

  CONFIG_TEXT: [error] 305814#0: *853684 FastCGI sent in stderr: "PHP message: PHP Warning: fopen(/var/www/vhosts/example.com/httpdocs/wp-content/plugins/duplicate-page/duplicatepage.php): failed to open stream: No such file or directory in /var/www/vhosts/example.com/httpdocs/wp-includes/functions.php on line 478

• A website example.com is not accessible. One of the following errors is shown:

  CONFIG_TEXT: 502 Gateway error nginx

  ---

  CONFIG_TEXT: 500 Internal Server Error

Cause

Missing files from the domain or files names were changed.

Resolution

1. Restore the website from backup using Plesk Backup Manager.

2. If there is no available backup in Plesk, contact the website developer in order to restore the files.