The nature of the failure is thru a Business Routing rule that executes custom code to check if an HL7 field is in a Lookup table ( if ##class(Ens.Util.FunctionSet).Exists("Client",tHL7FieldValue)) - the value was there but it could not find it.  At the same time, I was accessing that same table and deleting non-related entries thru the Portal via Ensemble > Lookup Tables.  I would assume the Exists function should be able to do a read on the table even if there is a lock on it due to maintenance.  Is that not how Lookup table behave?