Plesk is not accessible with error 500: The FastCGI process exited unexpectedly, error code 0x00000000

Symptoms

• Plesk is not accessible:

  CONFIG_TEXT: HTTP Error 500.0 - Internal Server Error
  C:\Program Files (x86)\Plesk\admin\engine\php-cgi.exe - The FastCGI process exited unexpectedly

• If try accessing Plesk directly on the server while connected to it over RDP, the following detailed information is shown:

  CONFIG_TEXT: Detailed Error Information:
  Module FastCgiModule
  Notification ExecuteRequestHandler
  Handler PleskEngine-FastCGI-php
  Error code 0x00000000
  Requested URL https://localhost:8443/index.php
  Physical Path C:\Program Files (x86)\Plesk\admin\htdocs\index.php
  Logon Method Anonymous
  Logon User Anonymous

• The application pool PleskControlPanel and the site pleskcontrolpanel are started in IIS.

• Repairing Plesk site using Plesk Reconfigurator does not help as well.

Cause

PHP which is used for serving Plesk site (located in the directory %plesk_dir%admin\engine) is corrupted.

Resolution

1. Connect to the server using RDP.

2. Back up the directory %plesk_dir%admin\engine.

3. Locate or download the necessary MSI file which contains Plesk's PHP files.

   For example, for Plesk Obsidian 18.0.42 this file is C:\ProgramData\Plesk\Installer\cache\pool\regular\PLESK-WIN_18.0.42_8472\dist-windows\plesk-engine.msi (or C:\ParallelsInstaller\parallels\pool\regular\PLESK-WIN_18.0.42_8472\dist-windows\plesk-engine.msi) and can be downloaded from https://autoinstall-win.plesk.com/PANEL-WIN_18.0.42/dist-windows/plesk-engine.msi. 

4. Create a directory for extracting the files from MSI (for example, C:\tempMSI).

5. Unpack the MSI file found in step 3:

   C:\> msiexec /a C:\ProgramData\Plesk\Installer\cache\pool\regular\PLESK-WIN_18.0.42_8472\dist-windows\plesk-engine.msi /qb TARGETDIR=C:\tempMSI

6. Copy all files from the directory C:\tempMSI\Program Files\Parallels\Plesk\admin\engine to the directory %plesk_dir%admin\engine with replacing the already existing files.