Update shipping information for Sales Order

Hi I'm trying to set tracking number and ship date for Sales Order, but get an error:

You do not have permissions to set a value for element trackingnumbers due to one of the following reasons: 1) The field is read-only; 2) An associated feature is disabled; 3) The field is available either when a record is created or updated, but not in both cases.

My code looks like this:

   NetSuitePortTypeClient client = new NetSuitePortTypeClient();

   Preferences preferences = new Preferences();

   SalesOrder order = new SalesOrder();
   order.internalId = shipment.Order.ExternalTransactionId;

   order.shipDateSpecified = true;
   order.shipDate = DateTime.Now;

   order.trackingNumbers = "Tracking number";

   WriteResponse response;

   client.update(CreatePassport(merchantSettings), null, null, preferences, order, out response);