У вас есть дополнительные "
в конце строки.
cursor.execute("INSERT INTO Description (SrId, FieldName, FieldValue) VALUES (?, ?, ?) WHERE IN (SELECT * from Description WHERE SrId <>id AND FieldName<>iname AND FieldValue<>ivalue)", (id, iname, ivalue)")
Должно быть
cursor.execute("INSERT INTO Description (SrId, FieldName, FieldValue) VALUES (?, ?, ?) WHERE IN (SELECT * from Description WHERE SrId <>id AND FieldName<>iname AND FieldValue<>ivalue)", (id, iname, ivalue))