The text does state that certain city pairings can not be booked via aircanada.com but can be booked on the phone via AC reservations - the typical phone reservation fee is waived as well.

So not quite an IT fail since they already know certain pairings can not be booked on the website.

Still sucks though - I won't argue that since most other travel websites can book pretty much any kind of pairing you can come up with.