Vagrant Problem: Host only network collides with another device ‘utun0’

Problem
Got this strange problem when starting a Vagrant VM:

The host only network with the IP '10.1.2.2' would collide with
 another device 'utun0'. This means that VMware cannot create
 a proper networking device to route to your VM. Please choose
 another IP or shut down the existing device.

Solution
Switch off your VPN. Doh!