I believe to have identified with more precision the problem that I have
mentioned to the beginning of the discussion.
It seems that only for some magazines (in the example I have called them with
"An" where n=number) the httrack is able to get the address for the download
(http://www.zzap.it/explorer.php?album=An&immagine=Bn) while for the others
no, moreover the download of the pages (in the example I have called them with
"Bm" where m=number) is almost never complete (it usually reaches the page
B12).
(I mention these results to help you to improvement the HTTrack)
Regards