Additional uncaught exception thrown while handling exception.

<h1>Additional uncaught exception thrown while handling exception.</h1><h2>Original</h2><p>PDOException: SQLSTATE[HY000]: General error: 2006 MySQL server has gone away: SELECT * FROM {system} WHERE type = &amp;#039;theme&amp;#039; OR (type = &amp;#039;module&amp;#039; AND status = 1) ORDER BY weight ASC, name ASC; Array
(
)
 in system_list() (line 165 of /var/www/medhis/includes/module.inc).</p><h2>Additional</h2><p>PDOException: SQLSTATE[HY000]: General error: 2006 MySQL server has gone away: SELECT expire, value FROM {semaphore} WHERE name = :name; Array
(
    [:name] =&amp;gt; rules_get_cacherules_event_whitelist
)
 in lock_may_be_available() (line 167 of /var/www/medhis/includes/lock.inc).</p><hr /><h1>Uncaught exception thrown in shutdown function.</h1><p>PDOException: SQLSTATE[HY000]: General error: 2006 MySQL server has gone away: DELETE FROM {semaphore} 
WHERE  (value = :db_condition_placeholder_0) ; Array
(
    [:db_condition_placeholder_0] =&amp;gt; 14491652956812d478b259e6.79595211
)
 in lock_release_all() (line 269 of /var/www/medhis/includes/lock.inc).</p><hr />