Having trouble to shutdown your VirtualBox since you upgraded to OS X 9 (Mavericks)?
[Solved] Write a short bash script, to remove your virtual vboxnet(XYZ) network adapter, which causes this failure!
VBoxManage hostonlyif remove vboxnet<xyz>
VBoxManage hostonlyif create
Remember to make it executable: chmod +X <scriptname_xyz>
So all we do here is to remove our vboxnet<xyz> “host only” network adapter by executing this script after we tried to shutdown our virtual box machine!
The script successfully recreates the adapter with the “saved” settings… (<xyz> = 0…n in most cases write vboxnet0)