raise an error in sql server severity higher than 18
WITH is an optional clause that goes at the end of the RAISERROR. A few examples:

RAISERROR('Oops', 10, 1)
RAISERROR('Oops', 10, 1) WITH NOWAIT
RAISERROR('Oops', 10, 1) WITH SETERROR

RAISERROR('Oops', 19, 1) -- Fails with "Error severity levels greater than 18..."
RAISERROR('Oops', 19, 1) WITH LOG -- OK


Remember that severities of 20 and above will terminate the connection (won't even jump to a CATCH).