Shortcode error: The “rank_group”

You probably didn’t specify the points_type attribute. For example:

[wordpoints_user_rank points_type="points"]

You may find the documentation for this shortcode helpful.

Thank you for quick answer. I tried to add points_type="Author points" (in my case). The error has gone, but nothing appeared.
Then I created new Points Type “credits” and its appeared. I think it was that because of space between words Author points.

Try author-points instead of Author points.