If you are getting the following error after you've upgraded to version 3.0 of Scotch Box:

default: Warning: Remote connection disconnect. Retrying...
default: Warning: Authentication failure. Retrying...
default: Warning: Authentication failure. Retrying...
default: Warning: Authentication failure. Retrying...

This sometimes happens with the upgrade. Try this in the Vagrantfile:

config.ssh.username = "vagrant"
config.ssh.password = "vagrant"