WooCommerce订阅API user_has_subscription（）不返回任何内容

I'm using the WooCommerce plugin for Wordpress and trying to make a page that validates the currently logged in user's subscription to a product (Product number 9). The user's subscription status is 'active' but this keeps never returns anything. I'm not sure what's going on or what to try next. The API docs are here: http://docs.woothemes.com/document/subscriptions/develop/functions/management-functions/

I'm testing the following code by visiting the page logged in as the user with the active subscription:

<?PHP
include('../wp-load.php');
$current_user = wp_get_current_user();
$SubCheck = WC_Subscriptions_Manager::user_has_subscription($current_user->ID, 9, 'active' );
if($SubCheck)
{
  echo "has sub";
}else
{
  echo "no sub";
}

The return value is supposed to be a BOOL.