Enabling dependent NuGet Libraries download during build - Visual Studio

"Enable NuGet Package Restore" from within Visual Studio, all of those third-party references will be added. I forget whether you can just right-click on the solution name to do this, otherwise look in Options -> Package Manager -> "Allow NuGet to download missing packages during build".

Original Post
http://our.umbraco.org/forum/developers/extending-umbraco/44227-why-many-references-are-not-found-in-source-code