vagrant启动报错Vagrantassumesthatthismeansthecommandfailed!

default: Guest Additions Version: 4.2.0 
    default: VirtualBox Version: 5.0 
==> default: Mounting shared folders... 
    default: /vagrant => C:/Users/Administrator/Desktop/www 
The following SSH command responded with a non-zero exit status. 
Vagrant assumes that this means the command failed! 

Stdout from the command: 

Stderr from the command: 

stdin: is not a tty 
chown: changing ownership of `/vagrant': Not a directory