Vagrant Machine index corrupted - win 8.1 - quick fix

Experienced an error after a successful vagrant halt and a reboot. On 'vagrant up', was greeted by the error: 'The machine index which stores all required information about running Vagrant environments has become corrupt. This is usually caused by external tampering..."

Easy fix was to navigate to /Users/{yourname}/.vagrant.d/data/machine-index and to remove both index and index.lock (both must be removed). rm index / rm index.lock.

Nice and easy. Vagrant up worked.