I have experienced the problem since I installed my machine with Ubuntu 13.10. If I hit the shutdown button, my laptop (Acer Aspire V5) executed a shutdown sequence. But after several seconds, it went on again. Then I found this website owned by +Thierry Nicola.
So I did the following step, as mentioned in the site: Open a terminal window
$ gksudo gedit /etc/rc.local.shutdown
the command will open the file /etc/rc.local.shutdown
Then I type this command in the file:
rmmod ehci_hcd
Next save the file.
Then try to shutdown your machine. It works fine in mine.