For example:
We get error to export_responses with this code:

$sid = 34798;
$sDocumentType = 'pdf';
$sLanguageCode='es';
$sCompletionStatus='all';
$sHeadingType='full';
$sResponseType='long';
$iFromResponseID=null;
$iToResponseID=null;
$aFields=null;
$result = $client->call('export_responses', array($sessionkey,$sid,$sDocumentType,$sLanguageCode,$sCompletionStatus,$sHeadingType,$sResponseType));

The error:
10.50.31.180 - - [27/May/2014:18:18:51 +0200] "POST /index.php/admin/remotecontrol HTTP/1.1" 500 27793 "-" "Zend_XmlRpc_Client"

And the external application show for example:
Fatal error: Uncaught exception 'Zend_XmlRpc_Client_HttpException' with message 'Internal Server Error' in C:\trabajo\lamp\pruebaslimesurvey\Zend\XmlRpc\Client.php:288 Stack trace: #0 C:\trabajo\lamp\pruebaslimesurvey\Zend\XmlRpc\Client.php(372): Zend_XmlRpc_Client->doRequest(Object(Zend_XmlRpc_Request)) #1 C:\trabajo\lamp\pruebaslimesurvey\zend_desarrollo.php(35): Zend_XmlRpc_Client->call('export_response...', Array) #2 {main} thrown in C:\trabajo\lamp\pruebaslimesurvey\Zend\XmlRpc\Client.php on line 288

Or with this code:
$sid = 34798;
$result = $client->call('export_responses', array($sessionkey,$sid,'csv'));

Or with this code:
$result = $client->call('list_participants', array($sessionkey,34798,0,10,false,false));