Booked yesterday an BA Avios+cash reward ticket for a AY flight HELBKK in C for November and sure enough I was not given a chance to choose my seat, but instead was automatically allocated seat 3A on this A330 new version - meaning it is a seatpair instead of a solo seat.

Could not change it on AY MMB - gives that error message. Called AY reservations today (answered within seconds), the lady said she could NOT change the seat beacause of it being a BA tkt, she would need to contact another department and would change the seat or call me. Within 30 mins it was changed to my preferred seat 2L.

But very strange indeed all these seating problems! And frustrating.