Have you tried to deactivate and reactivate the setting? If this isn’t working open the unity-greeter settings with an editor and add it there. You can do this by:
sudo gedit /usr/share/lightdm/lightdm.conf.d/50-unity-greeter.conf
It should look like this:
Just change it like that:
where ‘username’ has to be changed to your username, for example tejasbhagwat. Save the file and reboot.