Replying to my own post here...
I don't know anything about ruby, but seeing as the first line in the console output was an error concerning progressbar, I re-downloaded it and hey presto, everything works under linux/wine, (I haven't bothered tried it under windows).
Thanks for a great plugin by the way. About 80% of my work is building structures with arcs - steel frames for oval shaped cabins to be precise - and this is going to save me a ton of time.
Nick