In order to avoid getting logged out (and being unable to submit score), check the "Remember me" box when you log in. The forums are set to cut inactive members when they are inactive for 15 or 30 minutes (I'm not sure how long). When you play games you are in the same window and since you can't refresh while you're playing the forum thinks you're inactive.
Checking "remember me" means you're online all the time, no matter if you're inactive or even close the browser window... You'll never get logged out unless you click "log out" or delete cookies/temporary files.