This has been happening to me for week, but my lazy-level has decreased lately; Whenever I come to the forum index page and my browser cookies have been cleared, I'm asked to login, naturally. I attempt to do so on the forum index page, in the small area to the right under the banner, and no matter what, I'm told my credentials are wrong.
After it tells me my credentials are wrong, it takes me to the other page where logging in is the only thing underneath the banner. I'll then put the *same* credentials into that page, and it works fine.
In summary: login form on forum index is f00ked.