Php – Failed to load external entity

I am trying to integrate fedex API and getting this error .

Warning: SoapClient::SoapClient() [soapclient.soapclient]: I/O warning : failed to load external entity "../wsdl/RateService_v13.wsdl" in test.php on line 12

Fatal error: Uncaught SoapFault exception: [WSDL] SOAP-ERROR: Parsing WSDL: Couldn't load from '../wsdl/RateService_v13.wsdl' in D:\wamp\www\fedexapi\AddressValidationService_v4_php\php\AddressValidationWebServiceClient\rate_test.php:12 Stack trace: #0 D:\wamp\www\fedexapi\AddressValidationService_v4_php\php\AddressValidationWebServiceClient\rate_test.php(12): SoapClient->SoapClient('../wsdl/RateSer…', Array) #1 {main} thrown in test.php on line 12

<?php
// Copyright 2009, FedEx Corporation. All rights reserved.
// Version 2.0.0

require_once('../library/fedex-common.php5');

//The WSDL is not included with the sample code.
//Please include and reference in $path_to_wsdl variable.
$path_to_wsdl = "../wsdl/LocationsService_v3.wsdl";

ini_set("soap.wsdl_cache_enabled", "0");

$client = new SoapClient($path_to_wsdl, array('trace' => 1)); // Refer to http://us3.php.net/manual/en/ref.soap.php for more information

$request['WebAuthenticationDetail'] = array(
        'ParentCredential' => array(
            'Key' => getProperty('parentkey'),
            'Password' => getProperty('parentpassword')
        ),
        'UserCredential' => array(
            'Key' => getProperty('key'), 
            'Password' => getProperty('password')
    )
);

?>

How to solve this ?