我尝试了这里列出的许多答案，但这些都不能解决问题。最后，我不得不在Windows中的凭据管理器中删除“Windows凭据”下的VSCredentials_xxx条目，并重新启动Visual Studio 2019。

在那之后——在下一次VS启动时——VS终于向我要了代理凭证——在输入它们之后，Visual Studio就可以访问互联网了。

(似乎VS很久以前就存储了我最初提供的代理凭据-但因为在我们公司，他们在强制执行3个月后更改密码-凭据不再有效。)

我有一对Windows 2016服务器，其中Visual Studio无法连接到NuGet。在尝试了几乎所有其他建议的修复(注册表更改，Visual Studio/NuGet相关的缓存清理或文件/配置更改)后，以下是我们解决它的方法。

我们有一个组策略(GPO)，设置了密码，我将这些密码添加到我们的GPO密码列表中，以使其工作。

TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256

https://github.com/NuGet/Announcements/issues/60

在我的情况下，我有Fiddler运行，改变了我的代理设置

好吧，我尝试了上面所有的答案，希望我的注册表现在不是软管。但这似乎解决了我的问题:

https://learn.microsoft.com/en-us/answers/questions/959588/visual-studio-2022-won39t-connect-to-nuget.html

添加这个:TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384

到this中逗号分隔的字符串:

微软HKLM \ SOFTWARE \政策\ \ SSL加密\ Configuration \ \ 00010002

我希望这能帮助下一个希望在周六早上快速进行有趣的概念验证，然后花3个小时寻找解决方案的人!!

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 :)

我在Visual Studio 2015上执行Install-Package Modernizr时遇到了类似的问题。我通过以下步骤解决了这个问题:

Download the package from its online source. Go to Tools/NuGet Package Manager/Package Manager Settings. Select Package Sources from the window. Add a new package source by clicking on the + sign. Enter a name and source location by clicking on ... (triple dot) sign. Make sure that only the package source that you've just added is checked. Uncheck all the other package sources. Go to Package Manager Console and type Install-Package Modernizr. Visual Studio 2015 installs the package automatically and creates Scripts and packages folders in your root folder.

我希望同样的解决方案在安装其他包时也能起作用。