Bug fixed just now!!! Here's what happened:
If you were trying a guest checkout, the coupon code didn't work.
If you have a registered account, but you weren't logged in, the coupon code didn't work.
Now the coupon code will work and it doesn't matter if you are logged in and it doesn't matter if you do a guest checkout. The coupon code is for the VikingDigital.com site.
Sorry about the mess up! The coupon code worked for me when I tested it yesterday, but I was logged in with my test user account.