Xamarin.Forms Quickstart Tutorial : Error The type or namespace name 'App' could not be found

Hi,
I'm trying to use Xamarin.Forms and I'm following the Quickstart tutorial (https://developer.xamarin.com/guides/xamarin-forms/getting-started/hello-xamarin-forms/quickstart/).
I'm having an error "The type or namespace name 'App' could not be found (are you missing a using directive or an assembly reference?)" when trying to build the project.
I'm using Visual Studio 2013, I installed Xamarin.Forms, updated it from the manage NuGet menu.
I tried to add "using PhoneWord" in my MainActivity.cs without any success.
I verified that the PhoneWord checkbox is checked in Add -> Reference -> Solution -> Project for my PhoneWord.Droid and PhoneWord.iOS project.
I made sure to Set PhoneWord.Droid as StartUp Project

All the code come straight from the tutorial.

Any help ?
Thanks.