passwd permission denied even for root on solaris

I tried to reset the password of the local account but encountered an error.

root@foo # passwd 
New Password: 
Re-enter new Password: Permission denied 

I'm a bit confused because I was login as root. I checked /etc/nsswitch.conf and passwd was configured on ldap.

passwd: compat
passwd_compat: ldap

I found out I need to use -r to point passwd to files instead of ldap. So basically, my problem resolved by using passwd -r. If you are wandering what is -r, visit man passwd :-)