Originally Posted by
USFdonWill
From my understanding, the reason behind the issue is that your ticket is out of sync. When you get an upgrade on a UA flight, UA does not reissue the ticket to reflect the new class of service. On the other hand, CO will reissue a ticket when there has been an upgrade. Currently, this problem will persist till we are under one reservation system.
This may be true but I had another itin last month where CO was my first flight and UA on the second and third legs. I was waitlisted for upgrades on the UA flights so wanted to check in earlier so I had the edge if it came to a "tie breaker."
I still couldn't check in on line and had to wait until I got to the airport.