JsonRPCClient Not working some times

I'm trying to use Blockchain.info's JsonRPC API,

Code:

require_once 'jsonRPCClient.php';

$user = "************************************";
$pass = "***********";
$host = "rpc.blockchain.info";
$port = 443;

$url = "https://{$user}:{$pass}@{$host}:{$port}";
$rpc = new jsonRPCClient("{$url}");

It works with some methods such as getblockcount, like this:

$do = $rpc->getblockcount();
echo var_dump($do);

But it doesn't work on many methods such as getinfo:

$do = $rpc->getinfo();
echo var_dump($do);

(I get error: Undefined index: id jsonRPCClient.php on line 151)

What am I doing wrong here?

Am I missing something?