No key field found for creation of DataSource - Classification Datasource

Hello,

While trying to create a clasiffication datasource based on 0PLANT_ATTR, when i assign a characteristic and push the DataSource button, i get the following message:

No key field found for creation of DataSource

Diagnosis

During generation of a classification or configuration DataSource, only those key fields for the object table (field "Obj.Tabelle") that are already present in the basis DataSource transferred to the extract structure. This is the case when none of the key fields of the object table were found in the structure of the basis DataSource.

System response

A DataSource cannot be created without key fields. The action was cancelled.

Procedure

Check whether you have selected the correct basis DataSource and object table. For more information, please see SAP Note 569849.

Do you know what can be the problem?

Thank you and regards