I tried as well for a few weeks and noticed some other errors (not only AY). At least looking for AMS --> HND/NRT awards (and viceversa).
- I get the exact same error ("Sorry there is a problem with booking this journey online...") in ba.com not only for AY awards, but also in mixed award JL+QR (no problem BA+JL or QR-only awards).
- In Iberia.com i also face errors when "scoring" QR-only itinerary awards.
I ended up calling BA and they quoted me the award i wanted (AMS-HND r/t) in Finnair for 34,750 avios each way in economy... now i will call back in 2 days for the taxes.