Zend Soap Client error: Failed to enable crypto

Question

Hey guys, I'm using the Zend Soap Client library to consume a webservice, like this:

$wsdl = "path_to_wsdl_file";
$client = new Zend_Soap_Client($wsdl);

$client->nfeRecepcaoLote();

And I'm receiving the following errors:

Warning (2): SoapClient::__doRequest() [soapclient.--dorequest]: Failed to enable crypto [CORE/vendors/plugins/nfe/vendors/Zend/Soap/Client.php, line 987]

Warning (2):SoapClient::__doRequest() [soapclient.--dorequest]: connect() failed: Unspecified error [CORE/vendors/plugins/nfe/vendors/Zend/Soap/Client.php, line 987

Does anyone know what it can possibly be? The host of the webservice is this:

https://homologacao.nfe.ms.gov.br/homologacao/services/NfeRecepcao

and I'm using PHP 5.2.6 and Ubuntu 9.10.

Best regards,

Zé