Insofar as I am aware, there is no way to invalidate another user's session. It would be a major security hole if you could. Imagine the damage that could be done if one user could sign on and then invalidate everybody else's session.
Perhaps if you explained what you are trying to accomplish, we might be able to suggest alternate methods to achieve the same end. [ March 13, 2007: Message edited by: Merrill Higginson ]