Hi. Good to hear from you again.
I had that problem with a Coke promotion about a year ago. I called them (don't remember the number) and the CSR that answered had me read the codes to her, and she manually credited them to the promotion. I think some of the codes are from specially marked packages and expected to be used for that promotion (although they're not specifically stated to be for that promotion), and so when the promotion expires their machine thinks the codes are expired as well.
Good luck. Which promotion are you doing, if I may ask? Something for the kids?