unable top add ppolicy_overlay.ldif

I'm using Ubuntu 12.04 server running OpenLDAP-2.4.28.

I'm following this tutorial HEREhttp://raerek.blogspot.com/2012/09/openldap-password-policy-on-ubuntu-1204.html

When I get to the step to add the ppolicy_overlay.ldif

I get this error:

ldapadd -x -D "cn=admin,cn=config" -w secret -f ppolicy_overlay.ldif adding new entry "olcOverlay={1}ppolicy,olcDatabase={1}hdb,cn=config" ldap_add: Other (e.g., implementation specific) error (80) additional info: User Schema load failed for attribute "pwdAttribute". Error code 17: attribute type undefined

What could the issue be?

future thanks!