Plugin Name

Well, GeePress uses rewrite, so check your Settings > Permalink page and make sure rewrite is enabled.

Make sure you've linked your Google+ and wordpress accounts, you can do that in your /wp-admin/profile.php page.

It may be because your theme is a bit old or doesn't use the new Wordpress standards. You have to modify your theme to use this function. In your comments.php file (or wherever your comments form is), you need to do the following.

1. Find the three inputs for the author, email, and url information. They need to have those ID's on the inputs (author, email, url). This is what the default theme and all standardized themes use, but some may be slightly different. You'll have to alter them to have these ID's in that case.
2. Just before the first input, add this code: <div id="comment-user-details"> <?php do_action('alt_comment_login'); ?>
3. Just below the last input (not the comment text area, just the name/email/url inputs, add this: </div> That will add the necessary pieces to allow the script to work.