Welcome to FT.

Sometimes I have trouble using the online check-in on 1 of my home computers (of course the one hooked to the printer), but am usually able to use others. Not sure if it is something in the cookies, or what is going on, but seems to only be UA.com where I have these types of issues.

Your error sounds different however. Maybe try to get a coworker/friend to check in for you on another computer--and just get a reprint from Mr Chicken at the airport.