CakePHP & Nusoap Error

<?php
ini_set('soap.wsdl_cache_enabled', 0);

class ServicesController extends AppController
{
    var $uses = array("Donation");
    var $components = array( "Email", "MatchingEvents" );

    function registerDonation($donation = null){
        $this->log('hit #1', 'donation');
        $this->autoRender = false;
        App::import('Vendor','nusoap');
        Configure::write('debug',0);
        Configure::write('Session.start', false);

        //init soap server
        $server = new soap_server();

        $endpoint = 'http://new.mysite.org.uk/services/registerDonation';

        //initialize WSDL support
        $server->configureWSDL('donations', 'urn:donations', $endpoint);

        //setup service type
        $server->wsdl->addComplexType(
            'DonationResult',
            'complexType',
            'struct',
            'all',
            '',
            array(
                'success' => array('name' => 'success', 'type' => 'xsd:boolean'),
                'msg' => array('name' => 'msg', 'type' => 'xsd:string'),
                'error_number' => array('name' => 'error_number', 'type' => 'xsd:string')
            )
        );

        //register the method to expose
        $server->register('register_donation',
            array(
                'ct_number' => 'xsd:string',
                'project_id' => 'xsd:int',
                'donation_amount' => 'xsd:decimal',
                'gift_aid' => 'xsd:boolean',
                'donation_mode' => 'xsd:string',
                'donation_type' => 'xsd:string',
                'donor_title' => 'xsd:string',
                'donor_first_name' => 'xsd:string',
                'donor_last_name' => 'xsd:string',
                'donor_email' => 'xsd:string',
                'donor_address' => 'xsd:string',
                'donor_country' => 'xsd:string',
                'share_contact_with_charity' => 'xsd:string',
                'receive_updates' => 'xsd:string',
                'TransactionID' => 'xsd:string',
                'unique_ID' => 'xsd:string'
            ),
            array(
                'result' => 'tns:DonationResult'
            ),
            'urn:donations',
            'urn:donations#register_donation',
            'rpc',
            'encoded',
            'Accepts the results of a donation to a charity or project on the Big Give web site'
        );
        $this->log('hit #2 - register_donation is inside registerDonation', 'donation');

        //This inner function is registered and then called (keep within outer function!)
        function register_donation(
            $ct_number = null,
            $project_id = null,
            $donation_amount = null,
            $gift_aid = null,
            $donation_mode = null,
            $donation_type = null,
            $donor_title = null,
            $donor_first_name = null,
            $donor_last_name = null,
            $donor_email = null,
            $donor_address = null,
            $donor_country = null,
            $share_contact_with_charity = null,
            $receive_updates = null,
            $transaction_id = null,
            $unique_id = null
        ){
            //App::import('Model', 'Donation');
            //$Donation = new Donation();

            $this->log('hit #3-register_donation called!', 'donation');
            $return = $this->Donation->add(array(
                'unique_id' => $unique_id,
                'ct_number' => $ct_number,
                'project_id' => $project_id,
                'donation_amount' => $donation_amount,
                'gift_aid' => $gift_aid,
                'donation_mode' => $donation_mode,
                'donation_type' => $donation_type,
                'donor_title' => $donor_title,
                'donor_first_name' => $donor_first_name,
                'donor_last_name' => $donor_last_name,
                'donor_email' => $donor_email,
                'donor_address' => $donor_address,
                'donor_country' => $donor_country,
                'share_contact_with_charity' => $share_contact_with_charity,
                'receive_updates' => $receive_updates,
                'transaction_id' => $transaction_id
            ));

            $log = $this->Donation->log . 'Result: ' . $return['msg'] . "\n";
            $this->log( $log, 'donation' );
            if ( isset($this->Donation->matching['events']) )
            {
                //Reserved donations should already have had their events handled
                $this->MatchingEvents->handle($this->Donation->matching, !$this->Donation->matching['reserved']);
            }
            if ( !empty($this->Donation->cacheSaved) )
                $this->_sendDonationEmails($this->Donation->cacheSaved);
            return $return;
        }

        $HTTP_RAW_POST_DATA = isset($GLOBALS['HTTP_RAW_POST_DATA']) ? $GLOBALS['HTTP_RAW_POST_DATA'] : '';
        $server->service($HTTP_RAW_POST_DATA);
        $this->log('end','donation');
    }

    function _sendDonationEmails($donation)
    {
        //Send our email...
    }

    function testDonation($amount=1000, $unique_id=null, $ct_number=null, $charity_id=null, $project_id=null, $matched_campaign=null, $matched_cycle=null, $gift_aid='Y' )
    {
        // Simulates a test donation (Not via soap, but by inserting straight into db).
    }
}

?>