Log out from both the site and forum.
Log in only on the forum using the fields AlphaEclipse showed above.
The session time outs come from what has been explained above, you taking a long time to finish up your posts and the page you are on "times out" and needs to be reloaded. If you are not taking a long time to post however, and it happens on close to every message, it's more than likely due to you being double logged both on the site and the forum itself, they got a tendency to interfere with each other once in a while. I'd suggest just logging into the Site login next to the banner when you really have to(when resetting characters or uploading presets), otherwise just stick to the forum itself.