Accessing shared Windows folders in Sun (Oracle) VirtualBox

I've used Sun VirtualBox (Now Oracle VirtualBox) for a couple of years as a handy way to run Linux on my Windows-based laptop.  It broke a while back and I only just got around to reinstalling it using the new 4.0.0 release - and found shared folders didn't work out of the box.  I could set one up - and I could see it - but it wouldn't allow me access - I got the following error:

You do not have the permissions necessary to view the contents of "sf_virtualbox_sharename"

Python tkinter GUI - change default icon: Windows vs. Linux

I'm learning Python at the moment... and as part of that I've been looking at creating platform-independent applications.

The first step, I figured, was to get a basic window operating cross-platform.  I did this, no problem.  I did some reading on tkinter, which seems pretty straight forward (apart from being Tkinter in Python 2.x and tkinter in Python 3.x - note the case change - pretty annoying for converting apps from the old version).  So that was all good anyway.