Product ID is not defined in called script! Died.

I have this error message when I try to follow a link.

I have included the follow code pn the page that should pull up the article of choice. I took out my two lindes concerning the articleId. but this doesn't make a difference

<?php
include("/home/httpd/vhosts/xxx.com/httpdocs/amember/plugins/protect/php_include/check.inc.php");
$articleId = @$_GET["articleId"];
$page = @$_GET["page"];
?>

Once I am getting to the page I receive the following error message:

Product ID is not defined in called script! Died.

I have one product in the database. So this can't be the problem/

I saw in earlier message on the board that people should do something in the member CP. but i can't seem to find that. Where would I find this? or maybe i have something else that is wrong?

thank you in advance

Andrea