I am trying to implement passwordless authentication via ssh2. I have used the well documented technique of generating a key pair with a blank passphrase on my client machine, and installing the public key on the destination server (AIX 5.3) in the user's .ssh2 directory. I have used this technique successfully in the past on other flavours of Unix.

However when I connect (e.g. using sftp2) it still asks for a password, and I have to supply the user's Unix account password before it lets me in. What have I missed? Is there a setting somewhere else that is overriding those in the sshd2 config file?

well, these should be present on the server :
What the debug (-vv flag)says when you connect with sftp ? You can also try "-o PreferredAuthentications=publickey" when connecting.