Hey Joseph,
I have no experience with the Masso (so others may help you better than I can) but I know that the Masso has a function to surface the wasteboard, are you using it? It is → described here.
If you don’t use this function, but use a toolpath that you created with a CAM software, so if you want to machine the entire wasteboard, this means you go to the limits of the machine, so setting the zero point (either by probing, or by setting manually) on the workpiece is of crucial importance. If you set it only a millimeter away from the correct position you might have your toolpath shifted beyond the limits of the machine’s workarea, which would lead to a limits error.
The other thing is with Z. You say you are milling air. In order to use the paper method or to probe on top of the wasteboard, you must have your workpiece zero in your virtual 3D model on the top of the workpiece too. Remember, the coordinate you probe or set manually on the real workpiece has to be exactly where it is on your virtual 3D model’s zero coordinate.
Finally, if the machine “shuts off with alarm on the Z” or “shuts down mysteriously”, then this could be something to report to support@onefinitycnc.com
Got to go to bed now (past midnight in Central Europe), surely Masso users will further help you