I have several unused, unexpired $20 off R/T promotional codes that I received from this summer's Coca-Cola® 2011 'Twist Txt Win' Instant Win Game. When I try to use them now at southwest.com I get the following response:

Oops! The promotion code entered is not valid for one of the following reasons: the offer has expired, the travel and/or purchase dates entered are invalid, or information is missing to complete the request.

The codes are not expired and my desired roundtrip travel dates are more than a month from now during a non-blackout period. I've tried everything - changed the dates/cities just to see if I can get them to work for any period or city pair but still get the same response. I've tried over a half dozen unused codes but still no dice.

By the way here are the T&C's for the codes: 1. Southwest Airlines® $20 Fare Saver valid for one-time use at southwest.com or swabiz.com off the total amount of a Wanna Get Away roundtrip Fare purchase before taxes and fees. 2. Purchase must be made between May 9, 2011 and October 31, 2011 for travel from May 16, 2011 through January 14, 2012. 3. Blackout dates apply May 27, 2011 through May 31, 2011; July 1, 2011 through July 5, 2011; September 2, 2011 through September 6, 2011; November 22, 2011 through November 29, 2011; and December 15, 2011 through January 2, 2012. If any portion of travel falls on a blackout date the discount will not apply. 4. The discount is only valid with the provided Promotion Code and is not combinable with other promotion codes or fares available exclusively through the web tool "DING!". 5. 7-day or more advance purchase may be required. 6. Changes made to the itinerary after purchase may eliminate qualifications for this promotion.

I'm at wit's end, any ideas/suggestions?