Well, after removing all the “Expires” there is a big change. If we enter on: http://www.edinventa.com/checkout/?fill_cart=2841&apply_coupon=descuentosm
Then remove the item (or the discount).
Then enter again the same URL, the product is added (PERFECT!!!), but the discount some times is not (yes, some times I need to enter the URL three times, some times six times…).
Any guess? xD