In my test, I was using 2 products, one associated to the coupon the other not, here is a screen shot showing the cart.
I tried going to your site
and using the coupon code:
but that does not seem to apply to anything.
Maybe if you could send a screen shot of the coupon admin page showing the coupon settings, it would help me get a better idea. If you compress the screen shoot into a zip archive, it wont re size on upload.