Slitherine

I seem not to get this system.... According to the Slitherine Unified Login site, I have 3 users (Slitherine, Matrix and Matrix forums) unified. I log in automatically in this Unified Login Page.

I then have the option to go to the Slitherine site, to the Matrix site and to the Matrix forums.

If I go to the Slitherine site, I am not logged in. If I go from there to the Slitherine forums, I am logged in automatically. Some forum topics are linked to the Matrix forum. If I go to the Decisive Campaigns: Barbarossa page, for example, I am redirected to the correct Matrix forum. But logged in as guest. If I go to the Strategic Command WWII page, I get a message the I am not authorized to read this forum.

If I go from the unified login page to the Matrix site, I am logged in automatically.

If I go from the unified login page to the Matrix forums, I am not logged in (or rather, logged in as Guest).

As far as I remember, buying actually anything needs another login.... what am I doing wrong?

The unified system just ensures that you login in the sites using the same details.
So you have to login separately in each site.

Slitherine Member's:
https://www.slitherine.com/members/

Slitherine forum:
login_new.php?return_url=./forum/

Matrix Games Member's:
https://www.matrixgames.com/members/Default.asp?

Matrix Games forum:
http://www.matrixgames.com/forums/loginflat.asp

Also note that there isn't a Slitherine forum for Decisive Campaigns: Barbarossa, so you are redirected to the Matrix Games forum. Again you need to login separately, as it's another site and another account.
The forums were build with different languages, so there isn't a way to make the login process smoothly.