According to this thread:
http://askubuntu.com/questions/459840/lock-screen-not-working-14-04
this problem is likely due to a bug in gnome-screensaver, in that the 14.04 package does not configure it to run at startup.
According to this thread:
http:// askubuntu. com/questions/ 459840/ lock-screen- not-working- 14-04
this problem is likely due to a bug in gnome-screensaver, in that the 14.04 package does not configure it to run at startup.