Plugin issue in external php page

Hello,
everything is fine on my local machine but as soon as I upload to my server, I get the following error message:

PHP Fatal error: Class ‘MY_Analytics’ not found in /vhosts/production/httpdocs/portal/analytics/index.php on line 22

here’s the beginning of my external php page (based on https://cooltrainer.org/fixing-false-404-headers-on-external-pages-including-wp-blog-header-php/):

require_once('../wp-config.php');
$wp->init();  //set up the current user.
$wp->parse_request(); //Parse request to find correct WordPress query.
$wp->query_posts(); //Set up the Loop based on the query variables.
$wp->register_globals();  //Set up the WordPress Globals.
$wp->send_headers();  //Sets the X-Pingback header, 404 status (if 404), Content-type. If showing a feed, it will also send last-modified, etag, and 304 status if needed.
require_once('../wp-load.php');

Then line 22, I have
$MYA = new MY_Analytics();

It seems that my plugin is not loaded at this point.
How can I solve the issue?

Thanks