You may get an error, such as Authentication Token Manipulation Error, while trying to change passwords for a user. For example:
Authentication Token Manipulation Error
This error is being produced because you are using shadowed password files and the shadow doesn’t have entry for this user. i.e, /etc/passwd has an entry for this user, but /etc/shadow doesn’t.
In order to resolve this, you can either add the entry manually or recreate the shadow file. You can use pwconv to recreate the shadow file. See the manpage for more details on this.