I had the same error on Windows 8. It was fixed by following 2 advices! First restart docker and update environment
$ docker-machine restart default # Restart the environment
$ eval $(docker-machine env default) # Refresh your environment settings
This will create even more virtual connections in your Control Panel.
Next create an account @ hub.docker.com and log in docker in console:
$ docker login
Now you can pull images from hub.