Thanks for pointing to that. This is one of the most common technical problem that may invite a penalty. I had similar problem with one of my websites. I tried for different hacks to remove session IDs. I had at that time two different urls for my home page indexed (luckily not banned) - one with session ID and another without session ID.
Please read this discussion for removing session IDs
http://www.astahost.com/info.php/nee...rl_t11358.html