I am encountering an odd problem with su. Up until quite recently I was able to connect to one of my servers (CentOS-5.2) via ssh as an ordinary user and then, from the shell, perform an $ su -l to obtain root access. Now when I try to do this I see the following:

$ su -l Password: su: incorrect password

If, instead of I ssh to this machine as the root user ($ ssh -l root host) and enter exactly the same password from the same keyboard then I log in successfully as root. I have made no conscious changes to the target system configuration files and I know that the first method, logging in as a normal user and then su -l to root, was working just a few days ago. Review of the man and info pages does not enlighten me as to what might be wrong. The log file says this:

Jan 14 12:00:22 inet01 sshd[15433]: Accepted password for myuser from x.x.x.x port 53458 ssh2 Jan 14 12:00:22 inet01 sshd[15433]: pam_unix(sshd:session): session opened for user myuser by (uid=0) Jan 14 12:00:32 inet01 su: pam_unix(su-l:auth): authentication failure; logname=myuser uid=500 euid=500 tty=pts/8 ruser=myuser rhost= user=root

Any ideas as to what might be happening here and how I might fix it?

Regards,