I guess the question is where did your colleague purchase his ticket from, and did he actually have tickets that had the "HK" designator on them? [An invoice is not a ticket.] Was there a reconfirmation requirement? Could he not have called the travel agency that provided the tickets to intervene on his behalf? [Obviously he contacted you.] It is techically the Travel Agency's responsibility to ensure the passenger they have booked actually has seats on a given flight. I suppose I sound like an appologist for Air Canada, but you haven't provided enough information to make any other informed comment.