@LocutusOfBorg it worked now.
I was able to bring a VM up, access it via SSH, suspend it, resume it and finally halt it without any issues (I'm pasting the log below). Just tell me if you want me to test anything else.

Thanks!




vagrant up
Bringing machine 'default' up with 'virtualbox' provider...
==> default: Box 'williamyeh/ubuntu-trusty64-docker' could not be found. Attempting to find and install...
    default: Box Provider: virtualbox
    default: Box Version: >= 0
==> default: Loading metadata for box 'williamyeh/ubuntu-trusty64-docker'
    default: URL: https://vagrantcloud.com/williamyeh/ubuntu-trusty64-docker
==> default: Adding box 'williamyeh/ubuntu-trusty64-docker' (v1.12.1.20160830) for provider: virtualbox
    default: Downloading: https://vagrantcloud.com/williamyeh/boxes/ubuntu-trusty64-docker/versions/1.12.1.20160830/providers/virtualbox.box
==> default: Successfully added box 'williamyeh/ubuntu-trusty64-docker' (v1.12.1.20160830) for 'virtualbox'!
==> default: Importing base box 'williamyeh/ubuntu-trusty64-docker'...
==> default: Matching MAC address for NAT networking...
==> default: Checking if box 'williamyeh/ubuntu-trusty64-docker' is up to date...
==> default: Setting the name of the VM: devfactory
==> default: Clearing any previously set network interfaces...
==> default: Preparing network interfaces based on configuration...
    default: Adapter 1: nat
==> default: Forwarding ports...
    default: 22 (guest) => 2244 (host) (adapter 1)
==> default: Running 'pre-boot' VM customizations...
==> default: Booting VM...
==> default: Waiting for machine to boot. This may take a few minutes...
    default: SSH address: 127.0.0.1:2244
    default: SSH username: vagrant
    default: SSH auth method: private key
    default: Warning: Remote connection disconnect. Retrying...
    default: 
    default: Vagrant insecure key detected. Vagrant will automatically replace
    default: this with a newly generated keypair for better security.
    default: 
    default: Inserting generated public key within guest...
    default: Removing insecure key from the guest if it's present...
    default: Key inserted! Disconnecting and reconnecting using new SSH key...
==> default: Machine booted and ready!
==> default: Checking for guest additions in VM...
    default: The guest additions on this VM do not match the installed version of
    default: VirtualBox! In most cases this is fine, but in rare cases it can
    default: prevent things such as shared folders from working properly. If you see
    default: shared folder errors, please make sure the guest additions within the
    default: virtual machine match the version of VirtualBox you have installed on
    default: your host and reload your VM.
    default: 
    default: Guest Additions Version: 5.0.24
    default: VirtualBox Version: 5.1
==> default: Setting hostname...




vagrant status
Current machine states:

default                   running (virtualbox)

The VM is running. To stop this VM, you can run `vagrant halt` to
shut it down forcefully, or you can run `vagrant suspend` to simply
suspend the virtual machine. In either case, to restart it again,
simply run `vagrant up`.




vagrant suspend
==> default: Saving VM state and suspending execution...





vagrant status
Current machine states:

default                   saved (virtualbox)

To resume this VM, simply run `vagrant up`.




vagrant resume
==> default: Resuming suspended VM...
==> default: Booting VM...
==> default: Waiting for machine to boot. This may take a few minutes...
    default: SSH address: 127.0.0.1:2244
    default: SSH username: vagrant
    default: SSH auth method: private key
==> default: Machine booted and ready!





vagrant status
Current machine states:

default                   running (virtualbox)

The VM is running. To stop this VM, you can run `vagrant halt` to
shut it down forcefully, or you can run `vagrant suspend` to simply
suspend the virtual machine. In either case, to restart it again,
simply run `vagrant up`.




vagrant halt
==> default: Attempting graceful shutdown of VM...





vagrant status
Current machine states:

default                   poweroff (virtualbox)

The VM is powered off. To restart the VM, simply run `vagrant up`