Laravel Homestead "error while executing VBoxManage"

I'm having problems setting up Laravel Homestead. When I enter 'homestead up' inside GitBash I get the following error:

There was an error while executing `VBoxManage`, a CLI used by Vagrant
for controlling VirtualBox. The command and stderr is shown below.

Command: ["modifyvm", "29535830-0e33-4f82-a359-6973606f6529", "--natpf1", "delete", "ssh"]

Stderr: VBoxManage.exe: error: Code E_FAIL (0x80004005) - Unspecified error (extended info not available)
VBoxManage.exe: error: Context: "LockMachine(a->session, LockType_Write)" at line 529 of file VBoxManageModifyVM.cpp

My 'homestead.test' page is timing out when I try to load it. Here is my Homestead.yaml:

ip: "192.168.10.10"
memory: 2048
cpus: 1
provider: virtualbox

authorize: c:/Users/Aristophanes/.ssh/id_rsa.pub

keys:
    - c:/Users/Aristophanes/.ssh/id_rsa

folders:
    - map: c:/Users/Aristophanes/code
      to: /home/vagrant/code

sites:
    - map: homestead.test
      to: /home/vagrant/code/Laravel/public

databases:
    - homestead

Hosts

#   127.0.0.1       localhost
#   ::1             localhost
192.168.10.10   homestead.test

Can anyone help? Thanks.