<An error occurred while retrieving package metadata for \'bootstrap.3.3.5\' from source \'nuget.org\'. ========== Finished ==========
It requires two steps (second is maybe optional, but I always like clean solution)
In Explorer open folder where your project resides. Open packages.config using Notepad. Find and remove the line that mentions corrupted package name.
Open folder where your solution resides. Open subfolder "packages". Find folder with corrupted package and remove it.
Note: If you delete wrong package, just enable NuGet restore in Visual studio "Options", and while enabled, right-click solution and select "Restore missing NuGet packages"