Obtain Invoice Internal ID

I am doing something wrong here but IA m not sure what.  I cannot seem to obtain the internal ID of an invoice using the external ID.

Here is my code (its not the best, its just a temp project)

  private static String GetInvid(com.netsuite.webservices.NetSuiteService service, string externalID)          {              com.netsuite.webservices.RecordRef recordRef = new com.netsuite.webservices.RecordRef();              recordRef.externalId = externalID;              recordRef.type = ConsoleApplication2.com.netsuite.webservices.RecordType.invoice;              recordRef.typeSpecified = true;              com.netsuite.webservices.ReadResponse response = service.get(recordRef);              Console.WriteLine("Looking for externalID: -{0}-", externalID);              if (!response.status.isSuccess)              {                  System.Console.WriteLine("ERROR: {0}", response.status.statusDetail[0].message);                  return response.status.statusDetail[0].message;                }              else              {                  com.netsuite.webservices.Invoice invgot = (com.netsuite.webservices.Invoice)response.record;                    System.Console.WriteLine("Found Invoice internal ID of: {0}", invgot.internalId);                  return invgot.internalId;              }          }