[php] Error fetching http headers in SoapClient

I'm trying to invoke a WS over https on a remote host:remote port and I get:

Error fetching http headers

using the PHP5 SoapClient; I can get the list of functions by doing $client->__getFunctions() but when I call $client->myFunction(...) I always get this error.

I've googled and found that increasing default_socket_timeout in php.ini should fix it, but it did not work.

Can anyone suggest me a solution?

EDIT: here is the code:

$wsdl="myWSDL";

$client = new SoapClient($wsdl,array('connection_timeout'=>5,'trace'=>true,'soap_version'=>SOAP_1_2));

var_dump($client->__getFunctions());

try {
    $response=$client->myFunction("1","2","3");
         } catch (SoapFault $fault) {
    var_dump($fault);
    }
}

always ends in the error.

How do I solve the problem?