The log out page created by SecurityAssist uses the Clear Session Value server behavior from Cookies Toolkit. If Cookies toolkit is not installed when you run the SecurityAssist wizard, the log out page will not be created properly.
Once you have installed Cookies Toolkit, open the log out page. Go to the server behaviors panel and click the plus button. Select WA Cookies -> Clear Session value. Set it to Clear all and set the trigger to before page loads.