Thank you for your comments.
As I said in my original post, I did use the cheapest BOB, which as I also said, was probably the problem.
As to the rest of the components, they are working fine with an Arduino and GRBL, which suggests that the problem was with the parallel port and Bob combination. It was not my intention to denigrate Mach 3 or any of it many successful users.
Hopefully we can return to my original question - Has any member of this forum an actual experience of the Centroid Acorn Controller?