Some very helpful people on here, really very much appreciated - big thank you

I chose to go with Artcam as my mate uses it (a bit), another big thank you to HiltonSteve, he replicated my problem and confirmed there was an issue, he then went on to advise how to resolve but ended up doing it for me . Seems one numeric character was the culprit, with interesecting vectors :exclaim:

I cut the proto using mdf, which allows me to tweak the design ready for cutting in Aluminium and to incorporate other design changes that I know will be forthcoming.