Unable to access Plesk: syntax error unexpected '\' (T_NS_SEPARATOR) expecting function (T_FUNCTION) or const (T_CONST)

Symptoms

• Unable to access Plesk GUI with the following error message:
  

  CONFIG_TEXT: Server Error
  500 ParseError
  syntax error, unexpected '\' (T_NS_SEPARATOR), expecting function (T_FUNCTION) or const (T_CONST)
  Type ParseError
  Message syntax error, unexpected '\' (T_NS_SEPARATOR), expecting function (T_FUNCTION) or const (T_CONST)
  File Abstract.php
  Line 40

• The same error is shown in an attempt to access Plesk > Subscriptions or Plesk > Tools & Settings > Application Vault pages.

Cause

Plesk upgrade was performed recently but the services sw-cp-server and sw-engine were not restarted.

Resolution

1. Log into the server via SSH.

2. Restart sw-cp-server and sw-engine services with the command:

   # systemctl restart sw-cp-server sw-engine