password sync problem

[Jun Tanamal]

Hi!
I'm a newbie on this. This system had been setup by a guy before me.
Doing a testparm gives me one of these messages:
---cut----
ERROR: the 'unix password sync' parameter is set and the 'passwd
program' (/bin/
passwd) cannot be executed (error was No such file or directory).
---cut---

This might be the reason why I get logs such as this:
............
Nov 25 10:26:58 server PAM_pwdb[7980]: authentication failure; (uid=0)
-> myuser for samba service
...........

Can anyone tell me how to solve this?
Thanks in advance!!!

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Jun Tanamal