Rectangle wizard locks up and a pesky error on line 755

I was trying to mill out a rectangle with NFS rectangle wizard (I would presume an appropriate choice), and the first rectangle worked beautifully. Upon changing the dimensions for another rectangle the computer would either: lock up on NFS dimension input screen, display a box indicating that there was an error on line 755, or if I was persistant enough to push lots of keys, the code would post, sort of, and lock the computer at 50% CPU usage until I rebooted. I'm using 3.03 and am all legal with licenses and parking tickets paid. I'm at that "I don't know what I don't know" stage. I can post more info if this isn't a quick "... you're a dummy.." answer. Additionally, I was able to machine the rectangles using TurboCad.
PS: I've been using Mach for three years with TurboCad 12 and their CAM add-on. It's a nice combination for the price. ($300 for both if you ask nice and are upgrading from any brand of CAD program)