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.
I had the same problem when compiling the standard Windows Phone Databound App template. Following steps worked for me:
%LOCALAPPDATA%\Microsoft\Phone Tools\CoreCon\
and delete the contents of the folders 10.0
and 11.0