This error indicates an object class violation. Likely none of the classes listed in the objectClass attribute are structural or multiple, unrelated, classes are structural in the entry. Check the schema.
2.0 didn't check for such violations. Later versions do. Unforunately, some versions (like 2.3) misreport these violation. Looks like a bug fix needs to be back ported....
As this comes up frequently, I've added an answer to the FAQ at: http://www.openldap.org/faq/index.cgi?file=1385
Kurt