When adding a coupon in Back Office and you enter a Minimum value of 20.00 you get the error at the Pastebin link below. My coupon details are:

Coupon Name: $2.00 OFF
No Expiration Date
Coupon Type: AMOUNT
Discount on: ORDER
Minimum Value: 20.00
Coupon Value: 2.00
ENABLED
Never Expires

http://go.p-os.com/i