ssh public-private key logins issue
I'm having problems setting up public-private key authentication for one user. Circumstances are:
Linux box, (OpenSSH_4.1p1, OpenSSL 0.9.7g), attempting to ssh to an AIX box (OpenSSH_4.1p1, OpenSSL 0.9.7g), but keeps getting prompted for their password.
User on the linux box can ssh using public-private to other AIX boxes successfully. Other users on the same linux box can ssh to the AIX box using public-private keys without issue.
sshd_config on the AIX box that doesn't work for him is identical to that on boxes that do, and sshd has been restarted since the last update to its config, as has sshd on the boxes that do work.
Users authorized_keys file is identical (cksum) on the box that doesn't work to that on boxes that do, as are permissions on that file and the ~/.ssh directory.
I know that this user has been able to ssh to the AIX box before without being prompted for password, and do not believe there have been any changes to configurations or keys since then, but obviously I'm wrong.
Can't explain this and have for the moment run out of things I can think to check. Can anyone point me in the right direction?