No Clive, it was red wine not port (or sherry !)

The inputs were set as active, but on port 0. I just deactivated them (the red cross came to the rescue). I just have no idea why Mach3 should behave this way. Maybe it is a known quirk of the software. I copied the post nto the Artsoft forum to see if anybody closer to its' home might have experience of this. Anyway it is a problem solved, I just have to put the lids back on everything and start some cutting.

Cheers,
Rob