WordPress website on Plesk server is inaccessible: Error 500 PHP Fatal error: Unknown: Failed opening required '/home/johndoe/public_html/example.com/wordfence-waf.php'

Symptoms

• WordPress website example.com is inaccessible. The following error is shown in browser:
  

  CONFIG_TEXT: Error 500

• The following error is present in /var/www/vhosts/example.com/error_log:
  

  CONFIG_TEXT: AH01071: Got error 'PHP message: PHP Warning: Unknown: failed to open stream: No such file or directory in Unknown on line 0\nPHP message: PHP Warning: Unknown: failed to open stream: No such file or directory in Unknown on line 0\nPHP message: PHP Fatal error: Unknown: Failed opening required '/home/johndoe/public_html/example.com/wordfence-waf.php' (include_path='.:/opt/plesk/php/7.1/share/pear') in Unknown on line 0\n', referer: http://www.example.com

Cause

File wordfence-waf.php referred by user.ini of WordPress website is missing. As result WordPress engine fails to run website.

Resolution

1. Connect to the server via SSH.
2. Open the file /var/www/vhosts/example.com/httpdocs/.user.ini with command line text editor and comment out the line containing reference to wordfence-waf.php:

   Before edit:

   CONFIG_TEXT: auto_prepend_file = '/home2/example/public_html/example.com/wordfence-waf.php'

   After edit:

   CONFIG_TEXT: ;auto_prepend_file = '/home2/example/public_html/example.com/wordfence-waf.php'

3. Save file and close text editor.