Hi Bevan - a couple of obvious/not so obvious questions.....
You have the correct drivers installed on your laptop (for the DKU-Serial cable)?
You have the same port chosen in the support tool as for the DKU cable in the laptop? (windows - check Settings/Devices/Ports and see which one has the DKU attached)
You have the baud rates ok?
You have the laptop on/ignition on/insert cable/check coms ports in that order?
Give that a go - if all else fails I've got a second DKU and USB cable set, not yet attached (I was going to try a DIY) that you could potentially have to try and connect. If you check
www.miataturbo.net, there's a guy there called Giff who sells the clone cables for about $60 delivered (from the UK).
Cheers.
Founder of the QLD Chapter of the Honourable Brothers of Dodgy.
Benefactor of the Perpetual Dodgy award - Inaugural year 2007.