archive error (no replies)

Hi,

we have piwik 2.9.0 installed. The errorfile states this error:

Stack trace:
#0 /.../libs/Zend/Session/Namespace.php(143): Zend_Session::start(true)
#1 /.../core/Session/SessionNamespace.php(31): Zend_Session_Namespace->__construct('CorePluginsAdmi...', false)
#2 ..../core/Nonce.php(39): Piwik\Session\SessionNamespace->__construct('CorePluginsAdmi...')
#3 /..../plugins/CorePluginsAdmin/Controller.php(374): Piwik\Nonce::getNonce('CorePluginsAdmi...')
#4 [internal function]: Piwik\Plugins\CorePluginsAdmin\Controller->safemode(Array)
#5 .....core/FrontControl in /www/htdocs/w00c8c52/piwik/piwik_alexianer_holding/libs/Zend/Session.php on line 443

The email of the cronjob states a fatal error after archiving of some websites (totoal 17 websites).
Fatal error: Uncaught exception 'PDOException' with message 'SQLSTATE[HY000]: General error: 2006 MySQL server has gone away' in Zend....
Fatal error: Uncaught exception 'Zend_Session_Exception' with message 'Session must be started before any output has been sent to the browser; ....

our htcaccess-file
php_value memory_limit 3072M
AddHandler php5-cgi .php

php_flag log_errors on
php_value error_log "..../Errorlog/errorlog.txt"
php_flag magic_quotes_gpc Off
php_value max_execution_time 5000

The cronjob is set up like another one, which works fine!
Could somebody help me?