Usergroup problem

[gbpfan]

I have a specific forum on my board which I would like to keep private and only allow certain members to view. I created a new usergroup and members of that usergroup will have permission to view the specific forum. The problem is when I change the registered members to the new usergroup they are unable to access the specific forum and the main board itself.

These are the steps I go through when changing usergroups:

1. I go into the admin area and click on users.

2. I click search for users.

3. I click list top posters, then i pick a specific user.

4. I change their primary usergroup to "active user".

5. I click save.

After changing the usergroup and the "active users" are unable to access the main board. What am I doing to block this usergroup from accessing the board?