Comment 7 for bug 967241

I resolved a similar host freezing problem following this procedure:

  http://8thstring.blogspot.com.br/2012/01/error-could-not-locate-dkmsconf-file.html

After that I did:

  sudo apt-get remove virtualbox-4.1
  sudo apt-get install virtualbox-4.1

Problem solved, no more freezing.