Ubuntu 12.04 won't shut down - stopping winbind daemon

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http://askubuntu.com – My Precise Pangolin sometimes won't shut down - the screen is black with text on it. Mostly last line says something like "stopping winbind deamon" (sometimes also virtualbox, which is above winbind daemon) and it stays like this for about ten miutes. Then I usually hold the power button for >5s to shut it down. It's very unpredictable - sometimes the computer shuts down without problem and sometimes it hangs. I've tried many ways to shut it down: HW button, panel applet, sudo shutdown -h now, sudo poweroff, sudo halt, etc. even sudo reboot or restart from panel applet have this problem. Some (HowTos)