PASSWORD CHANGE

There is a checkbox on each user account that is called "User Cannot Change Password"

If that box is checked, then the users won't be able to change the setting. So, you can check the user accounts and unselect this setting.

If you have Active Directory enabled on your Domain, then you can modify this property with Group Policy. Go here for info on where in Group Policy to set this:
http://www.tburke.net/info/regentry/topics/GPRef.htm#93509

hope this helps

okay...
The best option which i do always is .. right click over my computer.. manage.. so that you will get computer management icon.. then click on local users and groups and then users. then.. right click on corresponding user.. then properties..

you can select the options..

users can change password
password never expires
account is disabled.. and more..

if u click on password never expires.. u wont find problem in changing the password.. otherwise just enable users can change password
you are done
;)

It's also possibly a bug in the version of Windows the domain controller or client is running. Is the client PC by any chance on Windows XP SP1? See http://support.microsoft.com/default.aspx?kbid=812530 - it's confirmed as a bug.