Problem with adding country attribute

Hi,

I am having problem with adding "c" country attribute. The error I got is:

ldap_add: Internal (implementation specific) error (80) additional info: no structuralObjectClass operational attribute

I'm running OpenLDAP 2.3.30. Here is related parts:

street: 123 Short St. l: Big Town st: Some State c: US ....

objectClass: friendlyCountry objectClass: Country objectClass: person objectClass: organizationalPerson objectClass: inetOrgPerson objectClass: posixAccount objectClass: shadowAccount objectClass: top objectClass: inetOrgPersonAccount objectClass: inetLocalMailRecipient

......

Is there something I need to add or change?

Simon