coupon codes

Hi guys

I am running through some checks of the website and it would seem my coupon codes are not working. I tried both ways, with a percentage and a value and none register when they are applied at the check out page. Once the coupon code has been applied, the page switches to the dashboard for a split second, says discount applied then goes back to checkout page with no amount changed.

Any ideas?

I dont have any screen shots as the page changes quickly, I have tried the plugin turn off as well