Plesk interface is not accessible: Class ‘pathtoclass’ not found

Symptoms

• Plesk is not accessible with one of the following error messages in a web-browser:

  Server Error 500

  Call to undefined method Plesk_Mode::isExternalOwner()
  Type Error
  Message Call to undefined method Plesk_Mode::isExternalOwner()
  File login_up.php

  ---

  ERROR: Server Error 500 DI
  NotFoundException
  No entry or class found for 'PleskGraphQlService'
  Type DI NotFoundException
  Message No entry or class found for 'PleskGraphQlService' File Container.php Line 135

  ---

  Error: Class 'PleskEmailActivationEventListener' not found

  ---

  ERROR: Class 'ComposerAutoloadClassLoader' not found (autoload_real.php:23)

  ---

  ERROR: Zend_Exception: File "Zend/Db/Statement/Pdo.php" does not exist or class "Zend_Db_Statement_Pdo" was not found in the file

  ---

  ERROR: require_once(): Failed opening required 'vendor/autoload.php' (include_path='/usr/local/sb/include:/opt/psa/admin/plib:/opt/psa/admin/externals') (init.php:4)

  ---

  Warning: Unknown: failed to open stream: No such file or directory in Unknown on line 0
  Fatal error: Unknown: Failed opening required 'auth.php' (include_path='.:') in Unknown on line 0

• When accessing the Domains page, the following error message is shown in Plesk:

  Call to undefined method PleskSessionContext::getUser

• When creating a new subscription in Plesk at Subscriptions > Add Subscription or a new database at Domains > example.com > Databases > Add Database, the operation fails with:

  Zend_Form::isValid expects an array

Cause

The plesk-core package is corrupted.

Resolution