Uncaught exception thrown in session handler.

PDOException: SQLSTATE[HY000]: General error: 2006 MySQL server has gone away: SELECT 1 AS expression FROM {sessions} sessions WHERE ( (sid = :db_condition_placeholder_0) AND (ssid = :db_condition_placeholder_1) ); Array ( [:db_condition_placeholder_0] => _aF19437wQXq1qZdV19rJo-lwRA_3UM_9T5GI6Np9UM [:db_condition_placeholder_1] => _aF19437wQXq1qZdV19rJo-lwRA_3UM_9T5GI6Np9UM ) in _drupal_session_write() (line 212 of /var/www/sscom/includes/session.inc).