It is a notice, not an error... so it may be that you just have notices turned off on the actual website and displayed on your local computer.
You have a recordset: rsUsers defined on the top of the page that you aren't using, so you wouldn't notice if the notice was simply not displayed the page would display fine.
That recordset is filtered with a sesison variable that isn't defined. There is no code on the page requiring that the user be logged in before seeing this page, and the recordset depends on a session variable that is probably set in the login process.
The solution is either to simply delete that recordset from the page because you aren't using it, or to require login in order to view this page.