There isn't a built in feature of the extensions that will allow you to do this. You could create a recordset using the group id to filter the recordset and then check if the recordset is empty or not. Then if its empty don't execute the insert. You can use the built in Dreamweaver functionality for the show if recordset is empty/is not empty to display the errors or the inserted results. This would all be done on the page that is posted to after the form is submitted.