UPDATE: This issue has now been resolved - please see moo.com is now my friend.
Donna passed a moo.com discount voucher on to me - it came with her first set of MooCards in the mail today. It was intended to be given to a friend - so she gave it to me.
Starry eyed and full of gratitude I went to the moo.com site and designed my cards - then duly paid for them and entered the promotion code. This is what I saw:
That error message again:

Just in case you can’t read the graphic, it says “Hello! It seems you’ve used moo.com before. It’s lovely to see you again, but we’re afraid this promotion is for new MOO customers only. Sorry about that.”
On my mother’s life, I have never been to moo.com before. Chances are, I never will again. Why offer a new customer promotion and then take it away arbitrarily? Of all the things that I’d test to ensure 100% flawless execution, that is right up there.
Having invested the time to design the card I put through the order anyway, but it leaves a bad taste in my mouth.
moo.com: FAIL

Complete and udder fail.
Susan,
thank you for your comment.
In effect, we’re talking about a $4.50 or so discount - it is not the money I am worried about, it is the fundamental cluelessness of yet another hip online retailer that has all the functional integrity of a beached jellyfish - 20 years of New Marketing, the world has changed, the consumer is your friend not your sheep to be shorn, blah blah blah, and we have a company that punishes referrals with a message that comes across as “I’m sorry, you are obviously trying to steal from us, please go away”. It beggars belief.
Best regards, Andrew