Did you figure out the problem? 

I'm trying to get this PHP based REST demo supplied by Salesforce to work to make sure I have a baseline working environment for a PHP project  based on OAuth 2.

I got as far as the Salesforce "front door" and authorized the token access and got the same error.

Error: call to token URL https://login.salesforce.com/services/oauth2/token failed with status 0, response

I checked my PHP error log and there is nothing in there to suggest a local environment issue. For example if it was a problem with Curl wouldn't it have generated an error in the log files? I also reran with the Console.app (Mac) running and no system error is logged.

The URL is:

https://localhost/resttest/oauth_callback.php?code=aPrxZibfVBKPF9v6C26GGbh_6Hcyjkmsijpu.3hFcQYVZEPyiAOLNtlysp3eU.VElSl3W759RA%3D%3D

The error is generated by the callback code comes from the following PHP snippet (full listing below):

$status = curl_getinfo($curl, CURLINFO_HTTP_CODE);

if ( $status != 200 ) {
    die("Error: call to token URL $token_url failed with status $status, response $json_response");
}

I checked info.php and the Curl is enabled on version 7.20.0 so I doubt it is a curl problem. What it suggests is that the Curl token request did not find the token. 

The Salesforce full source listing for the oauth_callback.php code is:

<?php
require_once 'config.php';

session_start();

$token_url = LOGIN_URI . "/services/oauth2/token";

$code = $_GET['code'];

if (!isset($code) || $code == "") {
    die("Error - code parameter missing from request!");
}

$params = "code=" . $code
    . "&grant_type=authorization_code"
    . "&client_id=" . CLIENT_ID
    . "&client_secret=" . CLIENT_SECRET
    . "&redirect_uri=" . urlencode(REDIRECT_URI);

$curl = curl_init($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);

$json_response = curl_exec($curl);

$status = curl_getinfo($curl, CURLINFO_HTTP_CODE);

if ( $status != 200 ) {
    die("Error: call to token URL $token_url failed with status $status, response $json_response");
}

curl_close($curl);

$response = json_decode($json_response, true);

$access_token = $response['access_token'];
$instance_url = $response['instance_url'];

if (!isset($access_token) || $access_token == "") {
    die("Error - access token missing from response!");
}

if (!isset($instance_url) || $instance_url == "") {
    die("Error - instance URL missing from response!");
}

$_SESSION['access_token'] = $access_token;
$_SESSION['instance_url'] = $instance_url;

header( 'Location: demo_rest.php' ) ;
?>

The oauth.php code is as follows:

<?php
require_once 'config.php';

$auth_url = LOGIN_URI
        . "/services/oauth2/authorize?response_type=code&client_id="
        . CLIENT_ID . "&redirect_uri=" . urlencode(REDIRECT_URI);

header('Location: ' . $auth_url);
?>

My local dev environment is:

OS X 10.6.6

MAMP Pro (with write all errors to logs)

PHP 5.3.2

Apache 

SSL enabled with self certificate (OpenSSL/0.9.7l)

Curl Enabled 7.20.0

Dreamweaver

Zend Framework

Salesforce DE (na7) version 20.0 (at time of writing Spring '11 not yet installed)

Any help would be appreciated!

Steve.