Google API - Refresh Token

I'm trying to get a new access_token after it has expired. I already have in the database the information I get as a return on the client's first access:

  

{"access_token": "TOKEN", "refresh_token": "TOKEN", "token_type": "Bearer", "expires_in": 3600, "created": 1320790426}

After this token expires I need to request a new one, I'm doing this:

$client = new Google_Client();
$client->setApplicationName(APPLICATION_NAME);
$client->setScopes(SCOPES);
$client->setAuthConfigFile(CLIENT_SECRET_PATH);
$client->setAccessType('offline');

$token['access_token']  = $db->dados[0]['access_token'];
$token['refresh_token'] = $db->dados[0]['refresh_token'];
$token['token_type']    = $db->dados[0]['token_type'];
$token['expires_in']    = $db->dados[0]['expires_in'];
$token['created']       = $db->dados[0]['created'];

$client->setAccessToken(json_encode($token));

if ($client->isAccessTokenExpired()) {
    echo "Expirado !";
    $client->refreshToken($client->getRefreshToken());
} else {
    echo "Valendo !";
}

The problem is that I always get this error message:

  

Error refreshing the OAuth2 token, message: '{"error": "invalid_grant"}