Clicking on other settings like Displays or Keyboards works fine, the new window opens and I can change the settings. But when I click on User Accounts, it does not open, and I am unable to click on anything else, and the window will not close and stays on top. I can't use anything else until I force log out. This is 14.04.4 LTS and Unity
This happens when you upgrade graphical stack and do not install
xxxx is your graphical stack name.
Check which version is installed by
dpkg -l | grep xserver-xorg-core
and see which line is with
ii xserver-xorg-core-lts-wily 2:1.17.2-1ubuntu9.1~trusty1 amd64 Xorg X server - core server
If it is
wily, then run
sudo apt-get install libwayland-egl1-mesa-lts-wily
and the issue will be fixed.