Auto Post on Twitter after authentication : getting Invalid access token error - twitter

Question

Here I need to automatically post on Twitter after authentication.
My code
<?php
session_start();
include("twitteroauth.php");
define('CONSUMER_KEY','zubLdCze6Erz9SVNIgG3w');
define('CONSUMER_SECRET','ZnZQ77bNnpBER2aSxTQGEXToAQODz9qEBSAXIdeYw');
define('OAUTH_CALLBACK','http://dev.pubs.positive-dedicated.net/Licensee/addPubEventWeekly.php');
/* Build TwitterOAuth object with client credentials. */
$connection = new TwitterOAuth(CONSUMER_KEY, CONSUMER_SECRET);
/* Get temporary credentials. */
$request_token = $connection->getRequestToken(OAUTH_CALLBACK);
/* Save temporary credentials to session. */
$_SESSION['oauth_token'] = $token = $request_token['oauth_token'];
$_SESSION['oauth_token_secret'] = $request_token['oauth_token_secret'];
switch ($connection->http_code) {
case 200:
/* Build authorize URL and redirect user to Twitter. */
$url = $connection->getAuthorizeURL($token);
header('Location: ' . $url);
break;
default:
/* Show notification if something went wrong. */
echo 'Could not connect to Twitter. Refresh the page or try again later.';
}
?>
and
ksort($_SESSION);
$tweet = new TwitterOAuth('zubLdCze6Erz9SVNIgG3w','ZnZQ77bNnpBER2aSxTQGEXToAQODz9qEBSAXIdeYw',$_SESSION['oauth_token'],$_SESSION['oauth_token_secret']);
print_r($tweet);
$account = $tweet->get('account/verify_credentials');
$message = "This is an example twitter post using PHP";
$postVal = $tweet->post('statuses/update', array('status' => $message));
But here I am getting "Invalid/Expired access token" Error.
I have changed twittreauth.php library file also from 1.0 to 1.1 from here
public $host = "https://api.twitter.com/1.1/";
Please suggest how to fix this