This should work, and I tried your first line of code in a new JS project with a new WinRT component in C#. It worked just fine. Can you show more of the whole C# class in your component as well as the JS code that's calling it?
Here's the .cs code for my test:
using System;
using Windows.Storage;
namespace Test2
{
public sealed class Class1
{
public async void TestAccess()
{
StorageFile file = await Windows.Storage.StorageFile.GetFileFromApplicationUriAsync(new Uri("ms-appx:///images/logo.png"));
}
}
}
And the JS code to call it:
var obj = new Test2.Class1();
obj.testAccess();
And have you also confirmed that the logo.png file is in your JS project?