extending open directory schema

I have used OpenLDAP in the past and was able to extend the schema fairly easily (download/edit schema file–drop it in /etc/openldap/schema add it to the list in /etc/openldap/slapd.conf) however when I try to extend the schema for open directory the server fails to start up (until the entry in /etc/openldap/slapd.conf is removed)

Any ideas–also as I will need to add the active directory connector later on I want to ensure that extending the schema will not cause this to fail.

Thsnk You