[Jon]

There are seperate forms on this page, one form is to update the cart etc., the other is to input the discount coupon. You can't embed the discount coupon form, inside the update cart form. To correct this, I move the update cart </form> and any associated form elements, up the page as high as possible. I then put the discount coupon code above the checkout button, and instead of using a form submission for the checkout button, I simply use text or an image that links to cart.php?mode=checkout.

Hope that makes sense.