E:\Ubuntu15>vagrant box add base virtualbox.box
==> box: Box file was not detected as metadata. Adding it directly…
==> box: Adding box ‘base’ (v0) for provider:
box: Unpacking necessary files from: file://E:/Ubuntu15/virtualbox.box
box:
An error occurred while downloading the remote file. The error
message, if any, is reproduced below. Please fix this error and try
again.

解决方案

在win10上安装最新的 Visual C++ 2010 ，安装完成重新执行就可以了。
下载地址：https://www.microsoft.com/zh-CN/download/confirmation.aspx?id=8328

E:\Ubuntu15>vagrant box add base virtualbox.box
==> box: Box file was not detected as metadata. Adding it directly…
==> box: Adding box ‘base’ (v0) for provider:
box: Unpacking necessary files from: file://E:/Ubuntu15/virtualbox.box
box: Progress: 100% (Rate: 855M/s, Estimated time remaining: –:–:–)
==> box: Successfully added box ‘base’ (v0) for ‘virtualbox’!

Vagrant up 失败，在Booting VM步骤就蓝屏了，这也是在Win10中安装很坑的地方。
解决过程：打开【程序和功能】->【启用或关闭Windows功能】->取消勾选Hyper-V选项，点击确定，重试即可。