"The system is running in low-graphics mode" when I try setup autorun numlock on

Ubuntu 14.04.
I like turn on numlock on autorun. I found this recommendation:

go to /usr/share/lightdm/lightdm.conf.d/50-unity-greeter.conf and add
greeter-setup-script=/usr/bin/numlockx on

When I did it, after restart I've got:
"The system is running in low-graphics mode". Any recommendation for this error not help me. But when I deleted "greeter-setup-script=/usr/bin/numlockx on" in /usr/share/lightdm/lightdm.conf.d/50-unity-greeter.conf all become ok! Why? do you know?