Nope. That’s weird! I think it’s not the One Page Checkout plugin as I guest because the same issue when I do the same with a different page like: http://www.edinventa.com/?fill_cart=2841&apply_coupon=descuentosm
First time it works with fill_cart. Then, if I delete coupon and product, that link does not work anymore.
Weird, weird, weird. I’m asking my hosting too. Maybe they can guess what’s happening!
Any other guess for your site? 🙁
Thanks so much in any case!!