Fatal error: Uncaught SoapFault exception: [Client] SOAP-ERROR: Encoding: object has no 'iId' property

Question

I'm trying to query a SOAP API and am receiving the above error. If I was to take a guess I'd say it's relative to this snippet from my wsdl file...

<!-- User authentication -->

    <element name="UserAuthentication">
        <complexType>
            <sequence>
                <element name="iId" type="xsd:int" />
                <element name="sPassword" type="xsd:string" />
                <element name="sType" type="api:UserType" />
            </sequence>
        </complexType>
    </element>

In getSoapResults() - do you have any idea where I'd put 'iId'? In fact, I'm not even sure what 'iId' relates to at this point, other than an integer of course.

<?php
public function getSoapResults() {

    $this->client = new SoapClient("http://api.example.com/v2/Example?wsdl");
    $this->header = new SoapHeader('http://api.example.com/', 'sAPIKey', '*************');
    $this->client->__setSoapHeaders($this->header);

    $oRefineByDefinition = new stdClass();
    $oRefineByDefinition->sId = 1203;
    $oRefineByDefinition->sName = '';
    $oRefineBy->oRefineByDefinition = $oRefineByDefinition;

    $aParams7 = array(
            "sQuery"        =>     "jeans",
            "bAdult"        =>  0,
            "iOffset"       =>  0,
            "iLimit"        =>  30,
            "oActiveRefineByGroup"  =>  $oRefineBy,
            "sColumnToReturn"   =>  array("sDescription","sBrand"));

   // print '<pre>';print_r($aParams7); die;

    $products = $this->client->getProductList($aParams7);

    print_r($products);
}

I've tried adding it to the '$aParams' array but this doesn't work.