Forms :: Updating Records When Using Subforms

I created a new form with two subforms. They each reference their own table but are linked by a field called Case_Name. I created a unbound combo box in the main form to allow filtering of the records based on Case_name and I do a requery when the record is found. I am importing data from another application into the three tables ( main with other fields, as well as other tables ..Case_Name only).

The form/subforms are then used to modify or add new data to the existing records in each table/subform. The problem I have is when I go to update/add data in the subforms, it comes back and tells me that it cannot add data due to data integrity. It thinks I am trying to add a new record with the same Case_Name. I have the forms and subforms set up as Data Entry = No so that no new records can be added. I only want to modify existing data as the records are created from the import process.