what version of security assist are you using?
It looks to me like you are using Security Assist 1. With Security Assist 1, we give you 2 extensions:
1) Security Assist
2) Cookies Toolkit.
you need to have cookies toolkit installed in order for the wizard to create the login page correctly. You login page is missing the Clear Session Value behavior, this happens if you run the Security Assist v1 wizard without installing Cookies Toolkit.
to fix the problem, install Cookies Toolkit, then on the Logout page add the Clear Session Value behavior. open the Server Behaviors panel, click the plus button and select WA Cookies -> Clear Session Value.
Set the trigger to before page load and select to clear all sessions.