TomAplomb - although what Will suggests will work, please do try entering as you were (ie from the calendar event) but without the route file upload. I am pretty confident that will work, as we can see that a successful entry was made earlier today (presumably without a file upload) but your confirmation/feedback would be very useful.
Unfortunately, this was working fine, but as part of today's release it looks like a setting got overwritten causing the upload error, it should be fixed tomorrow.
Thanks