Error OCS - when clicking on logout

Hi,

The OCS platform is generating the following error when I click to logout

DB Error: FATAL: terminating connection due to administrator command server closed the connection unexpectedly This probably means the server terminated abnormally before or while processing the request.
Stack Trace:
File: /var/www/html/ocsuis/lib/pkp/classes/session/SessionDAO.inc.php line 31
Function: DAO->retrieve(“SELECT * FROM sessions WHERE session_id = ?”, Array(1))

File: /var/www/html/ocsuis/lib/pkp/classes/session/SessionManager.inc.php line 160
Function: SessionDAO->getSession(“5kc84l5ncai5lqg9vk00b3lgm0”)

File: (unknown) line (unknown)
Function: SessionManager->read(“5kc84l5ncai5lqg9vk00b3lgm0”)

File: /var/www/html/ocsuis/lib/pkp/classes/session/SessionManager.inc.php line 60
Function: session_start()

File: /var/www/html/ocsuis/lib/pkp/classes/session/SessionManager.inc.php line 121
Function: SessionManager->SessionManager(Object(SessionDAO), Object(Request))

File: /var/www/html/ocsuis/classes/security/Validation.inc.php line 273
Function: SessionManager->getManager()

File: /var/www/html/ocsuis/lib/pkp/classes/core/PKPPageRouter.inc.php line 65
Function: Validation->isLoggedIn()

File: /var/www/html/ocsuis/lib/pkp/classes/core/Dispatcher.inc.php line 114
Function: PKPPageRouter->isCacheable(Object(Request))

File: /var/www/html/ocsuis/lib/pkp/classes/core/PKPApplication.inc.php line 170
Function: Dispatcher->dispatch(Object(Request))

File: /var/www/html/ocsuis/index.php line 65
Function: PKPApplication->execute()

What can be the error?

Thanks

David