OK - so the crux of my problem was that the folder I was working in was pretty far from my user folder. And some of the folder names had [ ] in them - so I think there were issues with the path.

Once I put the project into a folder at/near the top level of my user folder - with normal folder name - it was fine.

So... probably good to not that the path to the folder you are building should just be made up of normal characters.

As a wise old dev from the Sheffield office said - you live and learn ;)