It's not the same page as the forum itself, but a page which connects your ip to the game and therefore allows you to log in.
Make sure you don't have a proxy activated on your browser, as the website will register one ip and you'll be trying to log onto the client with anothet.
Wait 30-60 seconds before logging into the client, it's quite usual for it to not allow you to log in earlier as the website refreshes every 60 seconds and will need time to tell the client you're logging in.
Click the link I provided earlier. It's not the same as logging onto the forum.
Keep the page open while playing.
Hope this helps ya.