NuGet VS 2012 ServicePointManager does not support proxies with the https scheme

This also happens if you have a proxy setup in your internet settings.

I am not sure what happened in my nuget usage history but I end up stuck using proxy for my development machine. to make it work.

1- open fiddler

2- goto %AppData%\NuGet\NuGet.config

Package sources

<packageSources>
    <add key="nuget http" value="http://www.nuget.org/api/v2/" />
    <add key="nuget.org" value="https://www.nuget.org/api/v2/" />
</packageSources>

3- config

<config>
    <add key="HTTP_PROXY" value="http://127.0.0.1:8888" />
  </config>

4- profit.

The solution is in this answer:

Visual Studio 2010 nuget error: The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel

The problem is related to a bad SSL cert on the default Nuget package source.

I started getting this in VS2015 on one of my machines. I had an additional package feed on myget which constantly asked me for credentials and failed even when entering correct credentials. What helped me was clearing the nuget cache and config by deleting these two nuget folders:

• %APPDATA%\NuGet
• %LOCALAPPDATA%\NuGet

After that I restarted Visual Studio and added my custom package source again.