Во-первых, убедитесь, что вы используете последний Php Toolkit 20.0 .
Во-вторых, посмотрите полный пример:
require_once ('userAuth.php');
try {
$mySforceConnection = new SforcePartnerClient();
$mySoapClient = $mySforceConnection->createConnection(SOAP_CLIENT_BASEDIR.'/partner.wsdl.xml');
$mylogin = $mySforceConnection->login($USERNAME, $PASSWORD);
$fields = array (
'Status' => 'Completed',
'Description' => 'I wrote to you',
'Subject' => 'Message from Mr. X via Web .....',
'WhoId' => 'xxxxxx',
);
$sObject = new SObject();
$sObject->fields = $fields;
$sObject->type = 'Task';
$createResponse = $mySforceConnection->create(array($sObject));
var_dump($createResponse);
} catch (Exception $e) {
echo $mySforceConnection->getLastRequest();
echo $e->faultstring;
}