Seems the error has now been fixed.
Perhaps a different issue, but I just tried to check in for a flight and it told me I had only 1 seat to choose from! I'd looked not long ago at seats and there were plenty available, so I stalled and dropped out of the check in process.
Now if I go back to manage my booking I can see dozens of seats available, but if I want to select one I have to pay the $25 fee. To top it off, it says I'm checked in already even though I haven't got a boarding pass.
Probably my fault for dropping out of the check in process, but I didn't want to get stuck with a coughpy middle seat if there were others available!
Argh