就我而言，我在不知情的情况下注销了我的工作账户。重新登录我的visual studio帐户解决了这个问题。

如果有人仍然有问题，NuGet答案不工作。下面的答案对我(一家DevOps Azure托管TFS的公司)来说是有效的:登录和退出团队基金会。TFS和VS都报告为已登录，但情况并非如此。不得不辞职——与op描述的症状相同。详情请参阅此答案。

I had the same error message while scaffolding Identity to my ASP.NET Core MVC project. Since my connection was not behind a proxy, removing/editing proxy configurations didn't make sense. And I didn't want to delete a file or uninstall PMC either. While looking around I realized a "Clear All Nuget Cache(s)" button on Tools --> Options --> NuGet Package Manager --> General. After pressing the button I had to wait for some time for the operation to complete. After that I tried to scaffold the Identity again but it didn't work. Then I decided to restart VS and voila :)

在我的情况下，我失去了与Git的连接。我只是再次添加连接，它工作!：

也许这有帮助

对我来说，删除位于C:\Users\YourNameHere的.nuget文件夹解决了这个问题。

设置您的PC ->网络和互联网代理->自动代理设置然后 set“自动检测设置”为“关闭”，并清除“脚本地址”