Plesk panel fails to open: 500 Internal Server Error

Symptoms

• The Plesk panel cannot be opened:

  PLESK_ERROR: 500 Internal server error

• The same behavior is observed while trying to access any .php file inside %plesk_dir%\admin\htdocs\.

• The one-time login link command fails with:

  C:\> C:\Users\Administrator>plesk login
  The system cannot find the file specified. (Error code 2) at Unable to start ("C:\Program Files (x86)\Plesk\admin\engine\php.exe" -q "C:\Program Files (x86)\Plesk\admin\plib\cu\admin.php" --get-login-link -user admin)
  at (RunTime::Execute::start line 704)
  at Unable to execute CU(wmain line 64)exit status 1

Cause

The file %plesk_dir%\admin\engine\php-cgi.exe is missing.

Resolution

• Restore the missing file from other working Plesk server running the same version, e.g. 18.0.53.

Note: In case there is an Antivirus, the file might be restored from the quarantine and %plesk_dir% should be added to exceptions.

Additional information

Plesk is not accessible with error 500: Failed opening required