That's not an error. You should have done a changetype: replace rather than changetype: modify since it has no matching rule. This has been covered multiple times on the list over the years.
Err, changetype: modify with a replace action instead of an add action, even. ;)
--Quanah -- Quanah Gibson-Mount Product Architect Symas Corporation Packaged, certified, and supported LDAP solutions powered by OpenLDAP: <http://www.symas.com>