This problem related to the samba PAM module.
You have 2 solution at all.
Solution 1#: Remove it( as described below )
$ sudo apt-get remove libpam-smbpass
Solution 2#: Fix it( as described below )
Update your PAM authentication module by the following code and remove "SMB password synchronization"
$ pam-auth-update
References :
[1] http://ubuntuforums.org/showthread.php?t=2214042
[2] https://bugs.launchpad.net/ubuntu/+source/samba/+bug/1257186