无法在Current.LocalFolder中替换现有文件

Question

我有一个来自选择器的图像文件。我把它保存为'me.png'：

Windows.Storage.ApplicationData.Current.LocalFolder

如果我再次执行操作尝试使用新文件覆盖旧文件，则应用程序崩溃：

    An exception of type 'System.UnauthorizedAccessException' occurred in mscorlib.dll but was not handled in user code

Additional information: Access is denied. (Exception from HRESULT: 0x80070005 (E_ACCESSDENIED))

If there is a handler for this exception, the program may be safely continued.

我用来覆盖文件的代码是：

            await file.CopyAsync(Windows.Storage.ApplicationData.Current.LocalFolder, "me.png", Windows.Storage.NameCollisionOption.ReplaceExisting);

知道为什么会这样吗？它第二次崩溃在那行代码上。如果我将碰撞选项更改为GenerateUniqueName，它可以正常工作，因此覆盖文件似乎有问题。

更新

完整代码

    localSettings.Values["me_image_path"] = "Asssets/pinkBackground.png";
                 tile.BackgroundImage = localSettings.Values["me_image_path"];

var picker = new FileOpenPicker();
            picker.SuggestedStartLocation = PickerLocationId.PicturesLibrary;
            picker.ViewMode = PickerViewMode.Thumbnail;
            picker.FileTypeFilter.Add(".jpg");
            picker.FileTypeFilter.Add(".jpeg");
            picker.FileTypeFilter.Add(".png");

            StorageFile file = await picker.PickSingleFileAsync();

            if (file == null) return;
            await file.CopyAsync(Windows.Storage.ApplicationData.Current.LocalFolder, "me.png", Windows.Storage.NameCollisionOption.ReplaceExisting);

            localSettings.Values["me_image_path"] = "ms-appdata:///local/me.png";
            tile.BackgroundImage = localSettings.Values["me_image_path"];