Zend_Soap "Could not connect to host" Https

I have a problem using a webservice via HTTPS using Zend_Soap.

// create webservice
$client = new Zend_Soap_Client(WsdlFile);
// with certifikat
$client->setHttpsCertificate(serviceCert);

try {
// call webservice
    $result = $client->callFunctionIWant(); 
} catch (Exception $e) {
    error_log('Webservice error: '开发者_如何学编程 . $e->getMessage());
    $this->_redirect($this->getFrontController()->getBaseUrl().'/webservice/error/');
}

It works calling the werbservice locally, also without the certificate. It seems the live server can't connect. But using wget I can test the connection and see it working after installing the certificate on the server:

wget https://domain.of.server/service/service.asmx?wsdl --no-check-certificate
--2011-10-14 16:11:19--  https://domain.of.server/service/service.asmx?wsdl
Resolving domain.of.server... 192.168.0.23
Connecting to domain.of.server|192.168.0.23|:443... connected.
WARNING: cannot verify »domain.of.server« issued by `......':

Unable to locally verify the issuer's authority.
HTTP request sent, awaiting response... 200 OK
Length: 3326 (3,2K) [text/xml]
Saving to »service.asmx?wsdl«

100% [=========================================================================================== ==================>] 3.326       --.-K/s   in 0s      

2011-10-14 16:11:20 (857 MB/s) - »service.asmx?wsdl« saved [3326/3326]

What could be the issue that PHP is not able to connect to the host on the live system???

thx in advance Spanky