lightdm-gtk-greeter session loading fails

[mark]

I have installed lightdm-gtk-greeter. This worked fine for a while. When I tried to shift to unity-greeter (which I could not) and so reverting back to gtk-greeter it presents the login screen, where I enter password and enter: the screen is blank for 2-3 seconds and it loads the same login page. This repeats.

Ubuntu 14.04

here are the logs of /var/log/lightdm/lightdm.log http://paste.ubuntu.com/8816878/
/var/log/lightdm/x-0-greeter.log http://paste.ubuntu.com/8816910/

Previously I had the problem of The system is running in low-graphics mode in Ubuntu 14.04 and solved it by installing lightdm-gtk-greeter and uninstalling gtk3 (which i installed via sources: this was the major trouble before).

Now I am trying to shift to unity greeter and not able to do that. Please provide your support.