How to configure lightdm to allow manual logins in Ubuntu 14.04

Ok I finally found the solution, very simple. The file to edit is now located in /usr/share/lightdm/lightdm.conf.d, and is called: 50-ubuntu.conf.

I just added the line:

greeter-show-manual-login=true

and on next reboot I was able to input any user name on the login screen.

I also had the same issue with Ubuntu 14.04 installation. But I resolved the problem by following this site.

The solution is to create a file lightdm.conf inside /etc/lightdm/ and put the following contents in it:

[SeatDefaults]
greeter-show-manual-login=true

After a system reboot, I was able to login with other users.