Have you waited an unbelievably long time? I know for me on Linux with complex Fritzing sketches it causes the program unresponsive message and asks if I want to force it quit all the time and not just during Gerber export (ground fill, opening projects, updating, undoing things, etc). I ignore those messages as they are simply the system not getting a response from the program because it is busy doing the last thing you asked it to do, they are not a result of the program not doing what you want.
When I have to fix peoples Windoors computers I expect it even more and I just walk away and hope that when I come back a half hour later things have completed.