ESS - Updating "Family Member/Dependents"

We are on ERP2005 and are testing ESS.

We are unable to add a child in the "Family Member/Dependents" part of the Personal Information screen.

We have tried to update the table in "Define Active Subtypes and Application Case" in the IMG by adding subtype 2 to Infotype 21. However, we get the error "There is an inconsistency in the usecase maintained for this record" when we try to add the Infotype 21 with Subtype 2 - this error occurs with any value we try in the "Use Case" field.

Does anyone know how to add the facility to update (create/modify) dependents through ESS?

Thanks & Regards