cannot lock screen

ok so lock screen isn't working. weather I go to Main Menu -> Lock Screen or i click on the applet for lick screen it just makes a sound and nothing happens. im running ubuntu 9.10. And no im not using auto signon for GDM i have multiple users on my account. but its odd i cant figure out why it wont work. everything on the web is about the bug with the auto login. any help would be appreicated.