$ uname -a
Linux foobar-1 3.2.0-45-generic #70-Ubuntu SMP Wed May 29 20:12:06 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux
Distro is Ubuntu 12.04 LTS
More detail on the problem: Same thing happens on start VirtualBox and on start Skype. All these programs used to work before I switched to the proprietary NVidia driver (which I did in order to get support for multiple concurrent graphical user desktops). Now, switching back to the open-source one does not help.
Happens on Gnome desktop as well as Unity desktop. Changing users does not affect the issue. I have used `sudo unity --reset` and that seems to work, although it hangs on 'run key'. I have also used the Compiz dialog to reset to defaults. No indication of any issue in dmesg or in X.org logs.
It's bad when you can't start Gnu Emacs on your Linux box's graphical desktop.