snippet using constant contact - could not load class

<?php
// require the autoloader
require_once  $_SERVER['DOCUMENT_ROOT'].'/Ctct/autoload.php';

// does not work in modx 
use Ctct\ConstantContact;
use Ctct\Components\Contacts\Contact;
use Ctct\Components\Contacts\ContactList;
use Ctct\Components\Contacts\EmailAddress;
use Ctct\Exceptions\CtctException;



// Enter your Constant Contact APIKEY and ACCESS_TOKEN
define("APIKEY", "xxxxxxxxxxxxxxxxxx");
define("ACCESS_TOKEN", "xxxxxxxxxxxxxxxxxx");

$cc = new ConstantContact(APIKEY);

// attempt to fetch lists in the account, catching any exceptions and printing the errors to screen
try {
    $lists = $cc->getLists(ACCESS_TOKEN);
} catch (CtctException $ex) {
    foreach ($ex->getErrors() as $error) {
        print_r($error);
    }
}

// check if the form was submitted
if (isset($_POST['email']) && strlen($_POST['email']) > 1) {
    $action = "Getting Contact By Email Address";
    try {
        // check to see if a contact with the email addess already exists in the account
        $response = $cc->getContactByEmail(ACCESS_TOKEN, $_POST['email']);

        // create a new contact if one does not exist
        if (empty($response->results)) {
            $action = "Creating Contact";

            $contact = new Contact();
            $contact->addEmail($_POST['email']);
            $contact->addList($_POST['list']);
            $contact->first_name = $_POST['first_name'];
            $contact->last_name = $_POST['last_name'];

            /*
             * The third parameter of addContact defaults to false, but if this were set to true it would tell Constant
             * Contact that this action is being performed by the contact themselves, and gives the ability to
             * opt contacts back in and trigger Welcome/Change-of-interest emails.
             *
             * See: http://developer.constantcontact.com/docs/contacts-api/contacts-index.html#opt_in
             */
            $returnContact = $cc->addContact(ACCESS_TOKEN, $contact, false);

            // update the existing contact if address already existed
        } else {
            $action = "Updating Contact";

            $contact = $response->results[0];
            $contact->addList($_POST['list']);
            $contact->first_name = $_POST['first_name'];
            $contact->last_name = $_POST['last_name'];

            /*
             * The third parameter of updateContact defaults to false, but if this were set to true it would tell
             * Constant Contact that this action is being performed by the contact themselves, and gives the ability to
             * opt contacts back in and trigger Welcome/Change-of-interest emails.
             *
             * See: http://developer.constantcontact.com/docs/contacts-api/contacts-index.html#opt_in
             */
            $returnContact = $cc->updateContact(ACCESS_TOKEN, $contact, false);
        }

        // catch any exceptions thrown during the process and print the errors to screen
    } catch (CtctException $ex) {
        echo '<span class="label label-important">Error ' . $action . '</span>';
        echo '<div class="container alert-error"><pre class="failure-pre">';
        print_r($ex->getErrors());
        echo '</pre></div>';
        die();
    }
}

if (isset($returnContact)) {
    echo '<div class="container alert-success"><pre class="success-pre">';
    print_r($returnContact);
    echo '</pre></div>';
}