It's not a plane change, there's a bug in the system and a bad one. I was able to online change my LHR>EDI flight a few days before I flew on wednesday but when I tried on Thursday morning to move my return trip for today, it failed with the error above, when i called CS they moved me but the seat I wanted (1D on a domestic flight) had already gone in the 20 minutes it took them to do it so they put me in the seat behind. 2D.. Today, I go to check in for my flight on the iPhone App and the thing tells me I'm in 28B.. ...? I call up, they see the agent did what she said she did and confirmed it wasn't a plane change but they couldn't understand how I got bumped to the back of the plane.. They managed to get me onto an emergency exit row so I didn't have my knees around my ears....

I'm flying LHR > DUB on Sunday and I just went to move my seat and I got the same problem. They are shut now so fingers crossed the seat I want is still available tomorrow when I call and that I'm not sat right at the back when I check in...! Fix it please BA! It's not good for your customers..