In December I booked a straightforward domestic UA/CO award itinerary (SFO-MSY roundtrip, connecting in IAH both ways). After travel began, I changed my return flights twice; both times ran into IT related glitches: -First change - changed return from Dec. 13 to Dec. 14. Change displayed correctly on UA Web site. But the original booking was not cancelled on CO (CO Web site showed I was booked on both Dec. 13 and Dec. 14 flights). As a result, CO cancelled the entire reservation when I did not show for Dec. 13 flight. UA had to call CO to fix. -Second change - I wanted to change return from Dec. 14 to Dec. 16. Unfortunately I had already checked in online for my Dec. 14 flights. UA wouldn't help - said CO needed to cancel my online check-in first. CO's computer would not allow them to cancel my online checkin. Fortunately I was working with a very knowledgeable, professional CO RA who made the change for me, added a note to the reservation explaining the situation and asking the airport GA to fix the ticket, and noted that no change fee was due (UA does not charge a fee for short-notice changes to award bookings; CO does). Bottom line: When changing Star Alliance awards involving multiple carriers: -Double-check everything with all carriers (changes to these awards after origination of travel was not allowed until recently; some of the required IT support is still buggy). -Get to the airport early to allow time to sort out any issues.