之乎者也，阿彌陀佛

Open Internet Explorer browser, go to Internet Options/Security, select Local Intranet icon, click Sites button

On Local Intranet dialog click Advanced

and add your TFS server to the Websites list, like I did with mine (replace TFS with the name of your server)

Restart Visual Studio any enjoy NuGet from a new perspective!

This solution apparently solves all of the issues I had with the dreaded 401. Let me know if it works for you as well.

Considerations

The problem might not be related to NuGet at all but rather to PresentationCore (NuGet is a WPF application) which gets confusing results from OS through some interop. NuGet/Visual Studio is just a combination that triggers the otherwise sleeping problem.

 原文參考：http://blog.rthand.com/post/2011/08/26/Fixing-combination-of-NuGet-and-Team-Foundation-in-workgroup-configuration-401-Unauthorized.aspx