index type undefined

["Ronald Warner" <cscrw@mail.dlsu.edu.ph>]

i ran slapd -f myslapd.conf

now I am getting: 
myslapd.conf: line 30: index type "sn" undefined

thanks for your help.

below is my config:
include         /usr/local/ldap/etc/openldap/schema/core.schema
pidfile         /usr/local/ldap/var/slapd.pid
argsfile        /usr/local/ldap/var/slapd.args

database        ldbm
suffix          "o=itc, c=PH"
rootdn          "cn=admin, o=itc, c=PH"
readonly off
rootpw          secret

directory       /usr/local/ldap/var/openldap-ldbm
index cn eq,sn,uid   -------> line 30
index objectClass pres,eq