UWP SharpCompress Access Exception On Local Drives, Why?

Question

I'm trying to use SharpCompress to read .rar files from my UWP application. It works fine on network shares from which I can read the archive no problem, but I get System.UnauthorizedAccessException on files anywhere on the local system including for instance USB drives. I have access to the files by other methods e.g. StorageFile. It makes no difference whether BroadFileSystemAccess is on or off. I've tried in both C# and Vb.net Here's the code of my test app in C#. The exception occurs at ArchiveFactory.Open.

I can also read Zip files no problem using the .net Compression methods but they can't do rar files, hence needing SharpCompress.

using System;
using System.IO;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using SharpCompress;
using Windows.Storage.Pickers;
using Windows.Storage;
using SharpCompress.Archives;

namespace TestRAR
{
    public sealed partial class MainPage : Page
    {
        public MainPage()
        {
            this.InitializeComponent();
            OpenRAR.Click += OpenRAR_Clicked;
        }

        public async void OpenRAR_Clicked(object sender, RoutedEventArgs e)
        {
            FileOpenPicker picker = new FileOpenPicker();
            picker.FileTypeFilter.Add(".rar");
            picker.FileTypeFilter.Add(".cbr");
            picker.FileTypeFilter.Add(".cbz");
            picker.FileTypeFilter.Add(".zip");
            StorageFile pickfile = await picker.PickSingleFileAsync();
            if (pickfile == null) { return; }

            string pth = pickfile.Path;
            FileInfo pickInfo = new FileInfo(pth);

            try
            {
                ListRARs.Items.Clear();
                using (var Arch = ArchiveFactory.Open(pickInfo))
                {
                   foreach (IArchiveEntry a in Arch.Entries) 
                    {
                        string thisKey = a.Key;
                        ListRARs.Items.Add(thisKey);
                    }
                }
            }
            catch{ }

        }

    }
}

This is the first time I've used SharpCompress and I'm completely stumped. Any ideas anyone?