Why am I not able to request _GET_SELLER_FEEDBACK_DATA_ report from Amazon MWS Reports API?

I am using Amazon MWS Reports API to request and get Customer's Feedback using "_GET_SELLER_FEEDBACK_DATA_" report type. But unfortunately it says report status cancelled. But when I use scratchpad to request this report it works fine, following is my code please tell me what's wrong. The Reports API class methods i.e. invokeReportRequest() , invokeGetReportRequestList() , invokeGetReportList(), invokeGetReport() are as they are i haven't changed anything.

$report_type = "_GET_SELLER_FEEDBACK_DATA_";

$config = array(
    'ServiceURL' => "http://ift.tt/VsOShr",
    'ProxyHost' => null,
    'ProxyPort' => -1,
    'MaxErrorRetry' => 3,
    );

    $service = new MarketplaceWebService_Client($AWS_ACCESS_KEY_ID, $AWS_SECRET_ACCESS_KEY, $config, $APPLICATION_NAME, $APPLICATION_VERSION);

    $marketplaceIdArray = array("Id" => array($MARKETPLACE_ID));

    //Sends Report Request      
    $request = new MarketplaceWebService_Model_RequestReportRequest();
    $request->setMarketplaceIdList($marketplaceIdArray);
    $request->setMerchant($MERCHANT_ID);
    $request->setReportType($report_type);
    $request->setReportOptions('ShowSalesChannel=true');
    $request->setStartDate(new DateTime('-90 Days', new DateTimeZone('UTC')));

    $report_request_id = invokeRequestReport($service, $request);