SAP Message C1873 - Characteristic(s) not in knowledge base (modeling)

Diagnosis
In your configuration model, at least one characteristic is not in anyclass that is assigned to the configurable object (such as material).To display a list of these characteristics, choose Extras ->Display warnings.

System Response
Values assigned to these characteristics are not saved and are notavailable if you call the configuration again later.

Procedure
Assign the characteristics to a variant class that is assigned to theconfigurable object.