After some time a restarted playing around with my private vagrant setup when i came across this message, after trying to “up” my machines:
Your VM has become “inaccessible.”
So my setup is broken and I had to repair the machines. Luckily this is very easy:
$ vboxmanage list vms
There you can see the inaccessible vm and its id. Just unregister it and vagrant will be able to bring up your system from scratch.
$ vboxmanage unregistervm 652819f9-a4c4-4b18-b7e0-ea8e8bcec828
$ vagrant up
Bringing machine 'centos' up with 'virtualbox' provider...
[centos] Importing base box 'centos'...