The session has already been started. The session id must be set first

Question

We are getting this fatal error "The session has already been started. The session id must be set first." How can we close and destroy the user session, so they will have to login again before the error happens. Taken from Zend Sessions.php:

if (!self::$_unitTestEnabled && defined('SID')) {
        /** @see Zend_Session_Exception */
        require_once 'Zend/Session/Exception.php';
        throw new Zend_Session_Exception('The session has already been started.  The session id must be set first.');
    }