Error:You are not authenticated. Please run the Login function first

some days ago i was getting responce using this same code but now i m getting this error.
so whats the problem i dont know.
So please Help me to find the solution for this error

$soapUrl = "https://technet.rapaport.com/WebServices/RetailFeed/RetailFeed.asmx?wsdl";
$client = new nusoap_client($soapUrl, 'wsdl');

//prepare credentials:
$credentials = array(
'Username' => '*****',
'Password' => '*****');

$result = $client->call('Login', array('parameters' => $credentials), '', '', false, true);
$auth_ticket = $client->getHeaders();

$searchparams["Shape"] = "ROUND";
$searchparams["SizeFrom"] = "0.01";
$searchparams["SizeTo"] = "20.99";
$searchparams["ColorFrom"] = "D";
$searchparams["ColorTo"] = "K";
$searchparams["ClarityFrom"] = "IF";
$searchparams["ClarityTo"] = "VS2";
$searchparams["CutFrom"] = "EXCELLENT";
$searchparams["CutTo"] = "GOOD";
$searchparams["PriceFrom"] = "1";
$searchparams["PriceTo"] = "999999";
$searchparams["Page"] = 1;
$searchparams["PageSize"] = 20;
$searchparams["DiamondsFound"] = 0;

$client->setHeaders($auth_ticket);
$result = $client->call('GetDiamonds', array('parameters' => $searchparams), '', '', false, true);
echo '<h2>Result diamonds</h2><pre>';
print_r($result);
echo '</pre>';

Thanks