If you are running this on Windows, you must have ZipArchive. If you are running this on Linux and you do not have ZipArchive the plugin will use the command line zip utility--this is not the same as PHP's built-in zip. If you are on Linux, your provider may not give you access to the command line zip utility.
The instructions about the epub namespace apply to multi-user installations. They insure that only users with permission to create ebooks can generate ebooks. Otherwise any user could potentially get access to private documents. The plugin web site gives further specifics about security,
The reason you get the start button is one or both of:
1. You haven't created a namespace named epub and set its permission to 0
2. You are running as administrator which means you have universal access. So you can create an ebook from any namespace and any file name as long as the page id contains somewhere within it the string 'epub', as for instance a document named 'epub_test'.
".. and only if they have already been created and include the epub plugin syntax."
I don't follow what this means. How could anything appear on a page that hasn't already been created?
"The plugin keeps an internal list of these pages. If you wish to use an epub page for some other purpose, you can remove its name from the list using a second button which appears beneath the Start button and has the following label: Remove Page from Creator List. "
I don't understand what the purpose of this internal list is, and why I should ever need to remove a page from the plugin's list. Could you expand?
Plugins can insert elements into a page in various ways. The epub plugin checks to see if a page has been created in the epub namespace and if the user has permission to access this page. Then it checks to see if the page is in the epub list.
The list prevents the start button from appearing on pages in the epub namespace which are not epub pages, which would be both a bit of a pain and also confusing.
If you are in a multi-user environment, anyone with access to the epub namespace couid create a book from a page which appears on the list. So if you don't want other users to have access to your book and its contents, you have to take the page id off the list with the Remove button.