Estou recebendo o seguinte erro no zend framework:

Fatal error: Uncaught exception 'Zend_Controller_Dispatcher_Exception' with message 'Invalid controller specified (error)' in F:\wamp\www\helloworld\library\Zend\Controller\Dispatcher\Standard.php:245 
Stack trace: 
#0 F:\wamp\www\helloworld\library\Zend\Controller\Front.php(946):Zend_Controller_Dispatcher_Standard->dispatch(Object(Zend_Controller_Request_Http), Object(Zend_Controller_Response_Http))  
#1 F:\wamp\www\helloworld\library\Zend\Controller\Front.php(212): Zend_Controller_Front->dispatch()  
#2 F:\wamp\www\helloworld\web_root\index.php(10): Zend_Controller_Front::run('../application/...')  
#3 {main} thrown in F:\wamp\www\helloworld\library\Zend\Controller\Dispatcher\Standard.php on line 245

O que está causando isso e como posso corrigi-lo?