Milling Machine Multiple Heads

I'd say that the problem almost certainly lies in either how you have Artcam configured, and or the the file you made in Artcam.

As to the bounds of your file, The third line of your g-code is "G90G80G20G49" the G20 sets the machine to inches instead of mm. You need to change that to G21.

Thanks Todd
I'll try changing G20.