You could use the unmatched query wizard to build a query to show the
records in tablea not in tableb and a second query to show the records in
TableB that are not in TableA.
You can't have the query return an error message.
If you are trying to do this in VBA you could use the DLookup function to
see if any one number existed in TableA and in TableB.
Sample query to find unmatched records in TableA:
SELECT TableA.*
FROM TableA Left Join TableB
ON TableA.NumberField = TableB.NumberField
WHERE TableB.NumberField is Null