That's not on topic for this thread. In the future do not post off-topic into threads - create your own.
Pages http://en.support.wordpress.com/pages/ we bloggers create are static and adding them to the menu will not work because they will not update. You need to add the dynamic Categories pages created by the software that do update.
You can create a custom menu and add the dynamic Categories pages which are automatically created by the software when we publish posts, into the custom menu as a menu item
create custom menu http://en.support.wordpress.com/menus/
add dynamic category pages created by the software to it
Here’s a link to a custom menu walkthrough > http://onecoolsitebloggingtips.com/2011/08/11/wordpress-com-custom-menu-walk-through/
There are many common errors, misunderstanding and misconceptions when creating custom menus and you can read about them here > http://wpbtips.wordpress.com/2011/12/19/custom-menus/