In AD, open the user, Go to Account tab and under account options. Uncheck User can change password. They should be able to change passwords now.
** edit by Buddy Farr **
I believe Jirvine meant to say “remove checkmark from USER CANNOT CHANGE PASSWORD”. but there is another setting. when you have the account open and you find that the checkmark described above is unchecked then also go to the SECURITY tab and make sure that the CHANGE PASSWORD option has a checkmark in the ALLOW column and DOES NOT have the DENY checked. if the DENY is checked then it does not matter whatever else is checked it will not allow the user to change their password.
**end edit **