I think that you'll find that you've booked MAN/HKG, not ZRH/HKG, so you need to travel from MAN and you can't make your own way to ZRH, under a different reservation, and expect to check-in at ZRH for a departure from MAN.
It's a little alike a cheap return, you can't travel on the return unless you've travelled on the outward.
Welcome to the 21st Century!