The type or namespace name 'AppCallbacks' could not be found (are you missing a using directive or an assembly reference?)

Hi, I was building my project to Windows Store and I opened it in VS Express 2012 for Windows 8. I never got this error before, but in the VS Console it says: "The type or namespace name 'AppCallbacks' could not be found (are you missing a using directive or an assembly reference?)". I didn't get this error last time I builded for Windows. I have updated to Windows 8.1 since the last time I builded, so maybe that has something to do with it? I have the latest version of Unity running with -force-d3d11 Thanks, Andreas.