Website hosted on Plesk shows error: 500 Internal Server error: <handler> scriptProcessor could not be found in <fastCGI> application configuration

Symptoms

• Unable to access a website with the following message:

  PLESK_INFO: 500 Internal Server error: <handler> scriptProcessor could not be found in <fastCGI> application configuration

• The following error is observed with failed request tracing enabled:

  PLESK_INFO: ErrorDescription The FastCGI executable could not be found
  ModuleName FastCgiModuleNotification EXECUTE_REQUEST_HANDLER
  HttpStatus 500
  HttpReason Internal Server Error
  HttpSubStatus 0
  ErrorCode The system cannot find the file specified.

• There is a non-existent or incorrect path configured in IIS Manager > Sites > example.com > Handler Mappings > PHP-php > Executable (optional)

Cause

An incorrect executable path to the PHP handler is set for the website in IIS.

Resolution

1. Log into Plesk 
2. Re-apply PHP settings in Plesk > Domains > example.com > PHP settings > Ok (without any changes):
   

As an alternative, or if the solution did not help, update the path in IIS directly:

1. Connect to the server using RDP
2. Open IIS Manager > Sites > example.com > Handler Mappings
3. Double click on PHP-php handler and make sure that executable path is set properly.
   It might look like C:\Program Files (x86)\Plesk\Additional\PleskPHP54\php-cgi.exe. However, the path to the Plesk directory and version of PHP may be different.
4. Make sure that there is no other handlers for *php. Remove them if any.