As a follow up to my post I wanted to say that the problem was the interface cable. I bought another one, apparently exactly the same (silver and transparent housing) and same PCB but with the + line voltage sensed bridged (it powers up as soon as I insert the USB cable without having to insert the OBD side) but this one works and the DCAN utility sets it fine without errors. Evidently there are more versions of the same pcb layout circulating, some work and some don't (the PCB layout and components between the 2 is identical). The bag with which this came in however has a different marking on it and a FT232RL white sticker on one side - maybe not relevant (the driver was the same, but it did see it as a NEW COM port which I had to set again).