I have succesfully implemented REST API using oAuth in PHP application.

but i got error has occured during authentication.

Here with i showed my Coding

Initial request :

<?php

$token_url = LOGIN_URI . "/services/oauth2/token";
$curl = curl_init($token_url);
curl_setopt($curl, CURLOPT_HEADER, false);
curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
curl_setopt($curl, CURLOPT_POST, true);
curl_setopt($curl, CURLOPT_POSTFIELDS, $params);
curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, 0);

$json_response = curl_exec($curl);
$status = curl_getinfo($curl, CURLINFO_HTTP_CODE);

print_r($json_response);

?>

i get the Response :

Array
(
    [id] => https://login.salesforce.com/id/00D90000000Y2YTEA0/00590000000hoxcAAA
    [issued_at] => 1311080724805
    [refresh_token] => 5Aep8617VFpoP.M.4tKc.wsyE74IvVIhBvqtmPoh2taT_UxhUv_nV7O2gR6LBFQ_bixsqEhRzQ30w==
    [instance_url] => https://ap1.salesforce.com
    [signature] => FmkAs7jSP5HfV5XsSQDn+ONH+g0aO1uuS0Eso+YHzk4=
    [access_token] => 00D90000000Y2YT!AQ0AQAUzLVIubiAC7UnJtfo4V0r2gYQAwhr_5y6YkEJSX2R9Hc8JFgiPkYpCdh.RAz2BfdFKqg6sVfRhw6ct8g.f9zR32pab
)

using above access token, signataure i have formed the variable like

<?php

 $post_fields = array(
        'oauth_consumer_key' => '3MVG9Y6d_Btp4xp7PTQjzE8zY.4NJLD95rfMz3_fFk4_Oqb7ZMGMkx7CWHEVg3gRDhrtVUljTU3WZCnkvVWFo',
        'oauth_token' => $access_token,
        'oauth_signature_method' => 'HMAC-SHA1',
        'oauth_signature' => $signature,
        'oauth_timestamp' => $issued_at,
        'oauth_nonce' => $id,
        'oauth_version' => '1.0'
    );


   $token_url = "$instance_url/services/OAuth/u/v20.0";
    $curl = curl_init($token_url);
    curl_setopt($curl, CURLOPT_HEADER, false);
    curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($curl, CURLOPT_HTTPHEADER,array("Authorization: OAuth $access_token"));
    curl_setopt($curl, CURLOPT_FOLLOWLOCATION, TRUE);
    curl_setopt($curl, CURLOPT_POST, TRUE);
    curl_setopt($curl, CURLOPT_POSTFIELDS, $post_fields);
    curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, 0);

    $json_response = curl_exec($curl);
echo '<pre>';print_r($json_response);

?>

and i get the Error like

"LOGIN_OAUTH_UNEXPECTED_ERRORAn unexpected error has occured during authentication. Please try again."

anyone please help me to proceed further

thanks in advance