Invalid controller specified (robots.txt)

#0 /usr/local/lib/php5/ZF-1.9/Zend/Controller/Front.php(946): Zend_Controller_Dispatcher_Standard->dispatch(Object(Zend_Controller_Request_Http), Object(Zend_Controller_Response_Http))
#1 /var/www/www.sil-tre.it/app/classes/Bootstrap.php(31): Zend_Controller_Front->dispatch()
#2 /var/www/www.sil-tre.it/web/index.php(17): Bootstrap::run()
#3 {main}