'NOTHER UPDATE
To get things to work consistantly I have done the following.
From each folder that I installed different versions of Mach, right click on mach.exe, drag it to the desktop, create shortcut. Then edit the shortcut to look like this: >>> C:\Blah blah.exe /p MachMill<<<. Now I rename the shortcut so that I will know which version of Mach I am starting.
That's my story, and I'm stickin' to it.