Here's another data point. I just now tried to make a booking online in my BAEC account, with avios on Finnair. It saw availability and offered me a flight but when I clicked through I got the same error message as the OP. I rang the BAEC Gold line and explained; he tried to do it himself, and hit the same wall. After 40 minutes of faffing, mostly on hold, he came back and said 'OK, that'll be 35,000 avios and ... " Well, that simply can't be. It's a zone 4 flight, in economy, one way, which according to the chart should be 13,000 avios. (In fact, according to the chart, there is no category that costs 35K. Even zone 7 -- 5500+ miles -- is only 31,000.) He looked again but said he couldn't find any such chart that I was talking about. In the end, he gave me a booking reference and is going to send it to the rate desk for manual pricing. I have to ring back in two days.