So, after brilliant perseverance by John Brock and his Programmer, this problem is now fixed.
Really great help and support from John and his team.
From my understanding it turned out to be some sort of conflict/bug in the Sketchup/OS coding. Not 100% on that, but the CSV Export now works.
I have let John know, so I would assume that he will be uploading the new version to his website for download.