title: Vagrant error "Failed to mount folders in Linux guest" after halt or reload
body: <p>I'm trying to use a Vagrant box from someone else, and it works fine when I first start it, but after I stop it and restart it with either <code>vagrant halt</code> and <code>vagrant up</code>, or <code>vagrant reload</code>, I get the following error message:</p>
  
  <pre><code>Failed to mount folders in Linux guest. This is usually because
  the "vboxsf" file system is not available. Please verify that
  the guest additions are properly installed in the guest and
  can work properly. The command attempted was:
  
  mount -t vboxsf -o uid=`id -u vagrant`,gid=`getent group vagrant | cut -d: -f3` vagrant /vagrant
  mount -t vboxsf -o uid=`id -u vagrant`,gid=`id -g vagrant` vagrant /vagrant
  
  The error output from the last command was:
  
  /sbin/mount.vboxsf: mounting failed with the error: No such device
  </code></pre>
  
  <p>Right now, searching for this error message turns up a lot of people having trouble with a bug Virtual Box 4.3.10, but that's not the problem I'm having.</p>