After one connects to an OpenLDAP server and attempts to add, modify or delete an attribute, Error 18 (incorrect matching) is displayed.
An EQUALITY matching rule specifier missing in some attribute type definitions of the OpenLDAP schema. EQUALITY matchingrule is used by the server to perform value comparison and thus is expressly required for the mentioned operations. The absence of EQUALITY matchingrule makes it impossible to compare attribute values, which causes operation failure.
Open the attribute schema definition and add an EQUALITY matching rule specifier which best fits a particular attribute type.