Yellow Swordfish said
Going to need more detail.
The problem here is that there is no such thing as 'login to the forum'. A user logs in to the website and all of that is controlled by WordPress. If you have logged in to WordPress - i.e., the website - then you are logged in - as simple as that.
So can you describe in more detail what the issue is in the light of the above?
I can login to WordPress (i.e. get to /wp-admin/, have full access, no problems). When I go to the forum page, it reads, "Please log in to post." So, I repeated the login by clicking the login button at the forum site. It processes the login there, and I still end up with "Please log in to post."
At a guess, it seems like the forum isn't recognizing that I'm logged into the site, despite the rest of WordPress recognizing it.