Hi,
the Vista pendant has it own plugin, it has zero interaction with the ESS or the ESS plugin.
Mach4 has in the ScreenLoad script a function called GoToWorkZero(), and when activated it does as you'd suppose it would, namely go to
z=machine 0, x=work 0, y=work 0, a=work 0. I suspect you are having problems because Mach4 is excepting to drive all four axes, whereas you have three.
You need to get into the ScreenLoad script and delete/comment out the line that requires the A axis goto zero.
This is really Mach4 setting, or rather set-up. Its not anything to do with Vista, but rather the machine as it is set up.
Craig