Trying to create a simple record (Unexpected Error result!)

I am trying to create a single timeBill record using the add() method of the NetsuiteService class. I have tried associating the caseTaskEvent record, the customer record and the item record - ALL USING THEIR INTERNAL IDs found in existing timeBill records added through the Netsuite UI. I have also tried removing those associations and just using the employee record. In every single incarnation I get the especially unhelpful and maddening:  "Unexpected Error" as a result.

Here is my example code:

                 TimeBill tb = new TimeBill();                  tb.timeType = TimeBillTimeType._actualTime;                  tb.timeTypeSpecified = true;                  var time = new Duration();                  time.timeSpan = 0.25;                  time.unit = DurationUnit.hour;                  tb.hours = time;                  tb.customer = new RecordRef() { internalId = "xxxx" }; //job/client field with * in NS                  tb.memo = "test!";                  tb.item = new RecordRef() { internalId = "xxx"}; //service item * in NS                  tb.caseTaskEvent = new RecordRef() { internalId = "xxxx" }; //non-billable task in NS UI linked to customer/client/job *                   tb.employee = new RecordRef() { internalId = "xxxx"};                  WriteResponse r = _service.add(tb);                  StatusDetail[] status = r.status.statusDetail; //UNEXPECTED ERROR- YA!