Originally Posted by hans

Just did the same to two seats IAD-LHR using GPUs (and thanks to ExpertFlyer). Took a few minutes and the agent had to ask for help but we finally concluded that it was because I was logged into the reservation (no changes just watching). Once I closed the window, they went through fine and no issues at all from the phone agent - good service.

Only problem now is that one of the seat selections won't hold but that's a different thread.