Windows 8.1 problem App.GetResourceStream method

I have a problem with a method on windows phone. It reads an xml file and returns a string, the problem is that this method only works on windows 8 and not on windows 8.1. Here is the code:

public static String readFile(String path)
        {
            var resource = App.GetResourceStream(new Uri(path, UriKind.Relative));
            StreamReader reader = new StreamReader(resource.Stream);
            String arquivo = reader.ReadToEnd();
            return arquivo;
        }