在我的情况下，我有Fiddler运行，改变了我的代理设置

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 :)

当我试图浏览NuGet包时，我得到了同样的错误，以解决以下相同的步骤:

1-转到%appdata%\NuGet\NuGet.config

2-验证该配置中提到的url

3-删除不需要的url

4-重新启动visual studio并检查

该错误可能是由临时网络问题引起的，如果重试，该错误将消失。

你需要在Nuget中添加代理设置。配置文件。有关详细信息，请参阅此链接:Nuget配置部分和Nuget代理设置。

nuget restore 

and

msbuild /t:restore

两者都没有为我工作，因为同样的错误。但

dotnet restore 

完美的工作。试试