SAP Operation with "apply result to the cache option" set in SUP

Hi,

I've created a 'create' operation mapped on a SAP function module (remote). I get the following warning message: "The output record of the 'CREATE' operation 'HistoryDetails->OP_Insert()' with 'Apply results to the cache' option set does not contain the primary key columns".

How can a SAP record have a primary key? The record has one column with the same name of the primary key of the mbo, but the error doesn't disappear!

Someone can help me?