Well, here we are a few days later and still no reply from an Arturia rep to either this thread or another. I agree that this situation is very damaging for Arturia's reputation.
I can say that I've tried multiple times with Internet Explorer, Google Chrome and Mozilla Firefox to use my coupon code and I'm getting that same error message.
I think my next step might be to phone their California office. Anybody out there who lives at or near Westlake Village, California, want to go knocking on their door? Here's the address:
5776-D Lindero Cyn Rd #239
Westlake Village, CA 91362