Join Date: Aug 2011
Location: Barcelona, London, on a plane
Programs: IB+ Gold, TK E+, Hyatt Globalist, Marriott LTP, IHG Diamond
Posts: 14,170
Does Cathay offer a paid fare on that route? Probably not, given the distance and back-tracking.
Often IT systems can't price reward tickets if the operating airline doesn't actually offer a fare on that route. I would have thought BA could sort it manually though.