From an Altitude email this evening:
Thank you for registering for the Say “Ciao!” to 5,000 Bonus Aeroplan® Miles offer.
We experienced some issues during the registration process. You may have received an error message while trying to register, however, we can confirm that you have been successfully registered for the offer and can start earning Bonus Aeroplan Miles for travel to Milan, Rome or Venice.
We apologize for the inconvenience.
Thank you,
Air Canada
I had not tried to re-enter the contest since last evening, when every attempt was met by... Sorry!