Tracking Number field permissions

Hello,

I've been on hold for a total of 105 minutes with Netsuite phone support.  Maybe posting here will be quicker!

I am receiving the error

[Code=INSUFFICIENT_PERMISSION] You do not have permissions to set a value for element trackingnumbers due to one of the following reasons: (standard permissions reasons listed)

when trying to update the tracking number field on a Sales Order.  This was working a few months ago when I originally wrote this code.

SalesOrder so = new SalesOrder();
so.setInternalId(thisOrder.getInternalId());
so.setTrackingNumbers(thisOrder.getTrackingNumbers());
so.setShippingCost(thisOrder.getShippingCost());
WriteResponse write = _port.update(so);

Any thoughts on the cause of this?  I am logging in with an Administrator role.