I am checking from my local server
Previously it is working fine suddenly it stooped working, can i know where i am going wrong

<?php

require_once 'AuthorizeNet.php';
define("AUTHORIZENET_API_LOGIN_ID", "xxxxxx");
define("AUTHORIZENET_TRANSACTION_KEY", "xxxxxxxx");
define("AUTHORIZENET_SANDBOX", true);
$request = new AuthorizeNetARB;
$response = $request->cancelSubscription($subscriptionId);
print_r($response);
?>

O/p : AuthorizeNetARB_Response Object ( [xml] => [response] => )