How to fix unable to launch

Question

I get the error when I try to start ubuntu

unable to launch "gnome--session --session=ubuntu" 
X session --- "gnome-session --session=ubuntu" not found; 
falling back to defualt session.

Answer 1

Error because your desktop session has been messed up. You can recover by reinstalling.

Open virtual console by ctrl+alt+f1 and execute below it will work.

# sudo apt-get install --reinstall ubuntu-desktop
# sudo reboot