Cannot create machine on docker ubuntu

hi there i just learn how to install docker in ubuntu
i follow step by step on docs in docker website
until i get in this step (create manager and worker machine) https://docs.docker.com/engine/getstarted-voting-app/node-setup/
when i try run the command “docker-machine create --driver virtualbox manager” i got this error
Running pre-create checks…
(manager) No default Boot2Docker ISO found locally, downloading the latest release…
(manager) Latest release for github.com/boot2docker/boot2docker is v1.13.1
(manager) Downloading /root/.docker/machine/cache/boot2docker.iso from https://github.com/boot2docker/boot2docker/releases/download/v1.13.1/boot2docker.iso
(manager) 0%…10%…20%…30%…
Error with pre-create check: "read tcp 10.0.0.180:60242->54.231.120.195:443: read: connection reset by peer"
can somebody tell me wht it is
thanks