Updating SalesOrder Order and Record Status not working

Hello, I'm trying to update a sales order, using the SuiteTalk API:


//Update sales order test
            SalesOrder so = new SalesOrder();
            so.internalId = "136782";
            so.status = "_pendingBilling";
            so.shipDateSpecified = true;
            so.orderStatusSpecified = true;
            so.orderStatus = SalesOrderOrderStatus._pendingBilling;
           

            var writeResponse = p._service.update(so);

The response I get is:

Message: Invalid orderstatus reference key F.
Code : INVALID_KEY_OR_REF

:h_a_w:

Whenn I comment out so.orderStatus, I get a successful response from the update.  However, the status never gets updated.  I could not find anything in the documentation nor in the forums, so I'm hoping that someone could help shed some light as to what I may be missing.  Also, the following are my preferences: