亚马逊MWS:ListOrders访问被拒绝错误

昨天我的代码还在工作，今天当我再次检查时，它抛出了一个错误。我想从亚马逊印度获取订单，我已经使用了订单。ListOrders亚马逊MWS的API这里是我的代码：

$action = 'ListOrders';
        $params = array(
                    'AWSAccessKeyId' => $data['aws_access_key'],
                    'Action' => $action,
                    'SellerId' => $data['merchant_id'],
                    'SignatureMethod' => "HmacSHA256",
                    'SignatureVersion' => "2",
                    'Timestamp'=> gmdate("Y-m-d'TH:i:s.''0''0''0''Z", time()),
                    'CreatedAfter'=> '2014-08-31T18:00:00Z',
                    'CreatedBefore'=> '2014-09-23T18:00:00Z',
                    'Version'=> "2013-09-01",
                    'MarketplaceId.Id.1' => $data['marketplace_id']
                );
        // Sort the URL parameters
        $url_parts = array();
        foreach(array_keys($params) as $key)
            $url_parts[] = $key . "=" . str_replace('%7E', '~', rawurlencode($params[$key]));
        sort($url_parts);
        // Construct the string to sign
        $url_string = implode("&", $url_parts);
        $string_to_sign = "GET'nmws.amazonservices.in'n/Orders/2013-09-01'n" . $url_string;
        // Sign the request
        $signature = hash_hmac("sha256", $string_to_sign, $data['aws_secret_key'], TRUE);
        // Base64 encode the signature and make it URL safe
        $signature = urlencode(base64_encode($signature));
        $url = "https://mws.amazonservices.in/Orders/2013-09-01" . '?' . $url_string . "&Signature=" . $signature;
        //echo $url;exit;
        $ch = curl_init();
        curl_setopt($ch, CURLOPT_URL,$url);
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
        curl_setopt($ch, CURLOPT_TIMEOUT, 15);
        curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 0);
        $response = curl_exec($ch);
        // Create DOM object and load eBay response
        $responseDoc = new DOMDocument();
        $responseDoc->loadXML($response);
        $response = simplexml_import_dom($responseDoc);
        //$parsed_xml = simplexml_load_string($response);
        //echo $url;exit;
        echo '<pre>';
        print_r($response);
        echo '</pre>';
        exit;

响应：

SimpleXMLElement Object
(
    [Error] => SimpleXMLElement Object
        (
            [Type] => Sender
            [Code] => AccessDenied
            [Message] => Access denied
        )
    [RequestID] => 890a9075-2993-4063-be60-922c43bb8428
)

1. [Message] => Access denied错误表示什么？

2. 它昨天在工作，今天却显示错误，为什么？

3. 我该怎么做才能让它再次发挥作用？

4. 它正在亚马逊的草稿纸上工作

请帮我一下。提前谢谢。