I'm not sure exactly what is causing the crash but I have a pretty good idea. The same thing was happening to another user so I've added some new code to a build that I'll be putting out today which includes many other fixes and changes. It has yet to be tested and I've never been able to re-create the problem myself on any of my test computers. Try going into CNC/CAM settings and selecting the post-processor you wish to use just before exporting G-code. Keep an eye out for v1.33a which I'm putting out in the next few hours here after I tie up some loose ends and it should be fixed, but you should also be able to get G-code export to work with a bit of persistence. Also, try saving your project after confirming your post-processor, before you export G-code.