Source unreachable when using the NuGet Package Manager Console

Even though my Package Source was set to nuget.org in Package Manager Console, explicitly adding the -Source nuget.org argument fixed this for me.

So an example of use would be:

Install-Package Akka.net -Source nuget.org

Akka.net being your package that you want to install, its just an example here.

I'm not sure what can cause your issue, but there is indeed a way to override package sources on a per-solution basis, but only if you've enabled NuGet Package Restore on the given solution.

Once a solution has enabled NuGet Package Restore a folder called ".nuget" gets added to the solution. Under this will be a file called "NuGet.targets" that has an ItemGroup whose Condition is " '$(PackageSources)' == '' " like the one you'll see in the attached image.

If the ItemGroup is empty (or completely commented out, as in the illustration) then the solution will use a specific file that should be the same as the sources listed under TOOLS >> OPTIONS. But if you uncomment or add PackageSource items to that ItemGroup the solution will search the package sources listed and ONLY the ones listed.

You can change NuGet source from UI as well. Just change NuGet source to older version and it should work fine.

There seems to be still few bugs in VS 2015 related to api.nuget.org (v3).

I had to copy the default NuGet source in Visual Studio's options. With the copied source, I changed the URL from https to http. This resolved the problem for me.

Credit for this suggestion belongs here: https://nuget.codeplex.com/discussions/561075#PostDetailsCell_1354351, to "jpharris4".