There is no built-in limit to the size of the content of a book. More likely you merely arrived at the end of the current section, and tapping to go to the next page will load the next section. You can also see the section names by tapping the table of contents button (the book-shaped icon on the left side of the lower toolbar). While Stanza Desktop tried to automatically detect the book's natural chapter breaks when transferring books to Stanza iPhone, it isn't always able to do so successfully, and in those cases it will simply break the book up into arbitrary parts (whose length is usually around 70 pages) called "Part 1", "Part 2", etc. This is because very large individual chapters can be slow to load in Stanza iPhone, so breaking the book up into parts will help to speed up the book's loading.