When I try to download my 8 daily chapters, after I download the first, the server don't let me download any further, under the argumet that I've alredy downloaded my 8 daily chapters, but that is not true, in a week I've must downloaded 3 or 4 chapters max, because of this error, ¿what is happening?

Are you using a download accelerator?
Those basically open multiple download connections on same file, so it will register as multiple downloads.

You better write your own downloader, analyzing the page file names and downloading using the "download page" link, that is.