Password change problem

I cannot change the user password in Usermin. I have Authen-PAM installed, I already have "usermin file in "/etc/pam.d/" with required parameters. But if I try to change the password of an old account (account created before installing Usermin) I get error message "Failed to change password : Old password is incorrect". Obviously it is not. If I have the "passwd_cmd" set as "/etc/usermin/changepass" I get error message "Permission denied". Please help.