Dropbox PHP API错误

Question

I've been developing a music website that plays .mp3 files from a Public dropbox folder, and I think I've found a solution on how to get file names from a directory in Dropbox.The code I've found is:

$consumerKey = 'key';
$consumerSecret = 'key';

require_once "dropbox-sdk/Dropbox/autoload.php";

session_start();
$oauth = new Dropbox_OAuth_PHP($consumerKey, $consumerSecret);

$dropbox = new Dropbox_API($oauth);

$info = $dropbox->getMetaData('Public', true);
print_r($info['contents']);

The autoload.php is in the right directory, all necessary files are present.But the error I get is:

Fatal error: Class 'Dropbox_OAuth_PHP' not found in C:\wamp\www\api\index.php on line 10

Is there something I'm doing wrong?