Invalid frontend name for VirtualBox without GUI

[Paul Norman]

I've been experiencing an error with VirtualBox on FreeBSD 10.2-RELEASE.

When I try to start a VM with VBoxManage startvm I get the error

$ VBoxManage startvm "test_default_1449216719057_77821"
VBoxManage: error: Invalid frontend name: 'GUI/Qt'
VBoxManage: error: Details: code NS_ERROR_INVALID_ARG (0x80070057), 
component Machine, interface IMachine, callee nsISupports
VBoxManage: error: Context: "LaunchVMProcess(a->session, 
sessionType.raw(), env.raw(), progress.asOutParam())" at line 592 of 
file VBoxManageMisc.cpp

I am able to reproduce this with a clean install in a VM.*

I installed per-requisites with pkg and then emulators/virtualbox-ose
with ports. The config options I adjusted were to turn off
X11, QT4 (requires X11), NLS (requires QT4) and I used
vagrant to create the VM I tried to launch.

If I turn on the QT4 and X11 options, this error goes away. With
just X11, I still get it.

I would much rather not need to install X11 on my server. Are there
any known fixes for this error?

* Using Vagrant to run VirtualBox in a VM running in VirtualBox
set up by Vagrant feels slightly recursive