Sorry about that. In case anyone else hits this problem, here’s the solution. I was confusing the login password with the encryption password for the files in question; I’d missed the point that they don’t have to be the same. Somehow or other my login password got changed; I’ve no idea how that happened. I got a new login password, and, once logged in, I could decrypt the files with the original password. If, I now know, a file is encrypted with a different password from the login password, once you’ve successfully logged in and try to open the file, Axcrypt detects that the login password is incorrect and asks for the correct one.