When I bought the ticket I tried to book and pay for a preferred seat. It wouldn't work. After a couple of tries I called the agent and together we figured out that the seat map shown on the web site doesn't match the a/c type, hence the error message.

The flight is almost full, and they're just figuring this out now?
So she books me into a seat I want, which is a regular aisle seat near the back of the bus (no aisles available anywhere further forward). So no fee applies.
Then this message pops up when I check in and I'm slam-dunked into 16A, which doesn't recline due to the emergency exit row behind. Not b....y likely on a 5 hour flight. So I scramble and manage to snag an aisle seat across from the one I thought I had, which is now shown as occupied on the seat map, even though there are a dozen or so unassigned seats nearby. Not sure what happened, since there appears to be no change in a/c.
I'll be fascinated to see who I got bumped for.