For the benefit of others - I too got this error message checking in for a flight to Europe from Canada. I wasn't on any sort of upgrade/standby list (I'm not that fancy!). My ticket is a multicity Aeroplan rewards purchase, ticketed by AC (starts with 014). I just went to the airport and used a terminal without a problem. Still can't download the boarding passes via my AC app (the same error message pops up), but at least I got the boarding passes and seats I wanted :-)