Protect pages and their subpages with user name/password, and keep protected pages from showing up in menus, search results and page lists.
Not really, no. It depends on WordPress working as intended, and the user name and password is sent in clear text across the wire.
No, only pages and their subpages can be protected by this plugin.
Yes, that's actually considered a feature (at least for now). The point being, that a hidden page really doesn't need to be protected, and that it makes it work cleaner for e.g. members-only pages. Don't worry, as you have probably discovered, the contents of the page are not visible without the correct user name and password.
You might be running WordPress on PHP using CGI, and that often makes it impossible to handle the authorization features of HTTP - the appropriate headers simply don't get passed on to PHP/WordPress by the web server.
If you wan't to make sure that's the problem, try creating a protected post with a user name and password of debug/debug.
Great, thanks! Please do leave a comment on the plugin's homepage http://www.mfd-consult.dk/page-protection or send an e-mail with details; I'll make sure it's included in the next version.
If your question isn't answered here, please do leave a comment in the forum or on the plugin's homepage: http://www.mfd-consult.dk/page-protection