VS2015 - The 'NuGetPackage' package did not load correctly

Question

Just opened up VS 2015 Enterprise RTM, opened up an existing working project, getting the following error:

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Microsoft Visual Studio

Answer 1

Bear in mind

A reinstall of the NuGet Package Manager does NOT seem to remove the existing NuGet.Config file held in c:\users\name\AppData\Roaming\NuGet!

Mine had a missing 'packageSources' section (why, I don't know) but since this file was not recreated NuGet still didn't work!

So either manually enter this section or remove this config file, then reinstall NuGet through the Extensions and Updates which will recreate a brand new one!