MFC CRecordsets and primary keys

I've been trying to use CRecordsets with an ODBC connection in an MFC app (non-wizard created). I've just got to the point where I can add a new record but now it tells me that my changes cannot be made because they cause duplicates in the index, the primary key or the relationship. Now I can see this isn't true because I have an id value for exactly this reason, so my question is how do I fix it? Can I define the fields to be used as the primary key somehow? Or is there something else I can do?