Why the VS2013 App cannot get file in the App package?

Since the error says that the file can't be found I'd start by checking that the file is in the appxpackage. Make sure the database is flagged as content and to be copied to the output directory, and after building make sure it's in the AppX directory.

The error from GetFileFromPathAsync is because ms-appx:... is not a path and cannot be passed to that function.

--Rob