membership coupons

I have tried to offer a discount on my basic subscription, but I am getting this error message:

"The coupon you supplied is either invalid or expired."

I checked the expiration date and it's okay. As a test, I am using a 99% discount. Will the plugin not take such a high discount as a test?

Here's the register page: http://wordsandwriters.com/register/

And here is the test coupon code: testjoe

Could you look into this for me? Thanks, Joe.