I think that the correct code is
(set-option :print-success true)
(declare-datatypes () (( Data nil (cons (giorno Int) (mese Int)(anno Int) ))))
(declare-datatypes () (( Eta (cons1 (data Data) (io Int)))))
(assert (forall ( (e Eta) )
(and (< 0 (giorno (data e))) (> 0 (giorno (data e))))))
(check-sat)
and the output is
success
success
success
success
unsat