I\'m suddenly getting this error in my WP8 project, which seems to originate from generated code. I have a previous working version and the App.xaml is identical.
In my case I had this error after downloading and installing a fresh Visual Studio 2012 (the initial release version) and trying to build the default blank Windows Phone template project straight out of the box - it was only resolved by updating Visual Studio 2012 Express to Update 5.