Did you do the following, in this order?
1. Have the employee look up your phone number or scan your membership card (if you have one).
2. Have the employee scan the $30 coupon.
3. Ask the employee to enter the SKU for GCU (located on the coupon, 7 digits and starts with a "3", IIRC).
4. Wait for the employee to total out the transaction.
If you didn't do those things, in that order, that would explain your difficulty.
Yeah, i'm pretty sure they tried that. They followed the directions from the coupon. They even tracked down a card to scan just in case it had a different SKU (it was the same as on the coupon). Kept saying "already redeemed" according to them.
Don't worry, I'm sure it will work for everyone else just fine. I just have the worst luck ever with BB. Maybe I'll try a another store tomorrow....