adding new user problem?

I wan to add a new user. I have executed the following command. The user home directory is created.
but password creation shows error.
Note: I'm using LDAP Server for user authentication.

adduser xxx
Adding user `xxx' ...
Adding new group `xxx' (1003) ...
Adding new user `xxx' (1003) with group `xxx' ...
Creating home directory `/home/xxx' ...
Copying files from `/etc/skel' ...
passwd: Authentication token manipulation error
passwd: password unchanged
Try again? [y/N] 

If I run passwd command it shows the following error.

passwd: Authentication token manipulation error
passwd: password unchanged

What is the problem,How to solve this problem?

What operating system and platform?

I'm using Linux-Ubuntu.