PDOException: Integrity constraint violation: 1062 Duplicate entry

PDOException: SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry '1028-466-11375' for key 'PRIMARY': INSERT INTO {quiz_drag_drop_user_answers} (question_nid, question_vid, result_id, score) VALUES (:db_insert_placeholder_0, :db_insert_placeholder_1, :db_insert_placeholder_2, :db_insert_placeholder_3); Array ( [:db_insert_placeholder_0] => 466 [:db_insert_placeholder_1] => 11375 [:db_insert_placeholder_2] => 1028 [:db_insert_placeholder_3] => 0 ) in DragDropResponse->save() (rule 306 /sites/all/modules/contrib/quiz_drag_drop/quiz_drag_drop.classes.inc).