If you are the sa user when updating a user's password, do not provide any Old Password as this causes the error. Should the sa user need to change a user's password:
Click System, User Records (Ribbon menu) or System Control, Users, User Records (Classic menu).
Select the user's entry in the User list.
Click Options.
Click Edit.
Enter the New Password.
Click Save/OK. A dialog appears about OK to update User Details?
Click Yes.