For child orders I used to get the error referring to parent order unavailability until I arrived by way of experiment to a pause of a whopping 800 ms after parent order submission (to be fair, I do not remember trying to minimize this interval vigorously because I don't need to).
?
In addition to this my order placing synchronized queue is set to either wait for order submission confirmation from TWS or skipping 20 ms after order submission when confirmation cannot be expected (i.e. for orders with Order.Transmit = false).
?
--
Best,
DS
