I did notice that if you select a new tool from the drop down menu, the plunge rate changed to 0.006 and the tool path dosen't work. If change the plunge rate to a whole number (say 10 for example) the tool path display works.
This hit me doing a demo at Cabin fever. You are correct that a small value in plunge will be turned to a zero in the gcode 'pretty up' routines, and that will cause toolpath to fail.
I am looking for why the plunge value turns up so low. I recall fixing a problem in the plunge calculation using the material table overrride value. I suspect something there is causing this. Brian will (eventually) add an error message to the toolpath display when any gcode is bad.
I wont be able to compile a new version until Im home from NAMES on April 23, but I hope I have figured it out by then.