One of the following error messages appear in Plesk:
Error in Plesk: Zend_Controller_Exception: Session token has expired.
Zend_Controller_Exception: Permission denied.#0
PleskPermissionDeniedException: Session token has expired.
Suddenly Unexpected token < in JSON at position 0
The following message is logged in Plesk log file
# grep 'protection token check' /var/log/plesk/panel.log
ERR [panel] Forgery protection token check failed.
Sessions time for forgery protection token has exceeded.