ok so it appears to be a problem with Mach3 settings.
I reloaded Mach3 and poof, the gcode appears perfectly in the display window.
But then if I load the modified XML file that came with the BOB card... that one circle is gigantic.
So it definitely has to be a setting in Mach3
its this line in Gcode thats being misinterpreted: G2 X74.3 Y34.353 I-26.675 J9.747
Its supposed to be a circle 50.8mm in diameter, cut with a 6mm endmill... but it looks like it wants to cut a 500mm circle
Both XML files and the Gcode are attached.
I designed it in MM, and Mach3 is set to MM.