Internal Server Error when moving subscriber

[acuariano]

I get an Internal Server Error when I try to move a subscriber. This the code I'm using:

function move_subscriber($account, $subscriber_email, $list_id)
{
        print "moving to list $list_id\n";
        $listURL = "/accounts/{$account->id}/lists/{$list_id}";
        $list = $account->loadFromUrl($listURL);
        print "list found<br/>\n";
        print "Destination list: " . $list->name . " (" .$list->id . ")" . "\n";
        $params = array('email' => $subscriber_email, 'status' => 'subscribed');
        $found_subscribers = $account->findSubscribers($params);
        print "Found " . count($found_subscribers) . " subscribers. Moving first...\n";
        print $found_subscribers[0]->name  . ", " . $found_subscribers[0]->email . "\n";
        $found_subscribers[0]->move($list);
}

From the prints I know I got the target list and subscriber. But the last line in the function throws an error with no information. I went to oath_application.php and modified code in line 483:

        if($resp->headers['Status-Code'] >= 400) {
            $data = json_decode($resp->body, true);
            $message = var_export($data, true);
            throw new Exception($message);
            //throw new AWeberAPIException($data['error'], $url);
        }

With that I found that it's returning a 500 Internal Server Error.