Nuget Package - feed (VSTS) :Exception 'System.AggregateException' thrown when trying to add source

I have created a new feed with in Package Release hub (VSTS), installed the credentials, then added the package source.

Now, I am using Visual Studio 2015 to install Micrososft.Aspnet.mvc to a project, however it gives the following error:

Exception 'System.AggregateException' thrown when trying to add source
'https://mysite.pkgs.visualstudio.com/DefaultCollection/_packaging/MyLogUtils/nuget/v3/index.json'.
Please verify all your online package sources are available.    

I need to install NuGet packages normally, so I removed the feed from VSTS. However, the problem persists. How can this problem be resolved?

I met this issue today and fix it by following:

If you have delete the feed from VSTS, then you need to delete it from VS\Tools\Options\Nuget Package Manager\Package Sources:

If you didn't delete the feed in VSTS and want to use it, sign in with your VSTS team project account from VS upper right corner and restart VS:

This is may be an addition to the actual answer. I had to disable the check boxes as shown in below image to get the issue resolved. I think it might help to someone.

I had the same issue and I fixed issue by disabling my custom NuGet servers. Go to Tools->Options->Nuget Package Manager and disable your custom NuGet servers

Since this is the first Page I hit with my Problem:

If you get the error for nuget.org site, increase Version number:

https://api.nuget.org/v3/index.json -> https://api.nuget.org/v4/index.json

under Tools->Options->Nuget Package Manager (see Image from @Eddie-MSFT)

V3 doesn't seem to work since today.