I found this problem in the forum:

"after adding the "Prices for Logged-In Users Only" and "restricted_website" contribs, the add to cart button now does not work in the products listing page when a customer is logged in. The customer would need to go into the product information page in order to add the item into the cart. Does have a SSL cert cause this problem? Any suggestions? Which codes do you need to see in order to help me? Thanks in advance."

THE SOLUTION

The problem is that the modifcation made in file APPLICATION_TOP.PHP is incorrect.

FIND THIS CODE:
// customer adds a product from the products page
case 'add_product' : if (isset($HTTP_POST_VARS['products_id']) && is_numeric($HTTP_POST_VARS['products_id'])) {
$cart->add_cart($HTTP_POST_VARS['products_id'], $cart->get_quantity(tep_get_uprid($HTTP_POST_VARS['products_id'], $HTTP_POST_VARS['id']))+1, $HTTP_POST_VARS['id']);
}
tep_redirect(tep_href_link($goto, tep_get_all_get_params($parameters)));
break;
// performed by the 'buy now' button in product listings and review page
case 'buy_now' : if (isset($HTTP_GET_VARS['products_id'])) {
if (tep_has_product_attributes($HTTP_GET_VARS['products_id'])) {
tep_redirect(tep_href_link(FILENAME_PRODUCT_INFO, 'products_id=' . $HTTP_GET_VARS['products_id']));
} else {
$cart->add_cart($HTTP_GET_VARS['products_id'], $cart->get_quantity($HTTP_GET_VARS['products_id'])+1);
}
}
tep_redirect(tep_href_link($goto, tep_get_all_get_params($parameters)));
break;

and REPLACE WITH

// customer adds a product from the products page
case 'add_product' : if (!tep_session_is_registered('customer_id')) {
$navigation->set_snapshot();
tep_redirect(tep_href_link(FILENAME_LOGIN, '', 'SSL'));
}
else {
if (isset($HTTP_POST_VARS['products_id']) && is_numeric($HTTP_POST_VARS['products_id'])) {
$cart->add_cart($HTTP_POST_VARS['products_id'], $cart->get_quantity(tep_get_uprid($HTTP_POST_VARS['products_id'], $HTTP_POST_VARS['id']))+1, $HTTP_POST_VARS['id']);
}
tep_redirect(tep_href_link($goto, tep_get_all_get_params($parameters)));
}
break;

// performed by the 'buy now' button in product listings and review page

case 'buy_now' :
if (!tep_session_is_registered('customer_id')) {
$navigation->set_snapshot();
tep_redirect(tep_href_link(FILENAME_LOGIN, '', 'SSL'));
}
else {
if (isset($HTTP_GET_VARS['products_id'])) {
if (tep_has_product_attributes($HTTP_GET_VARS['products_id'])) {
tep_redirect(tep_href_link(FILENAME_PRODUCT_INFO, 'products_id=' . $HTTP_GET_VARS['products_id']));
} else {
$cart->add_cart($HTTP_GET_VARS['products_id'], $cart->get_quantity($HTTP_GET_VARS['products_id'])+1);
}
}
tep_redirect(tep_href_link($goto, tep_get_all_get_params($parameters)));
}
break;


It should work now (see attachment for full install)

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