I had the exact bug that you are getting. You will notice that he is giving you the same speech in the shooting range as when you first met him. So when he finishes the speech in the shooting range, he tries to move like he did when you first met him. But this time there is no where to move. I believe this is why the game crashes.I had to load a save game before I first talked to Rubble. If you initiate with the "lips" instead of clicking the pass on Rubble, then the error should not happen. I do not know of a way to fix the error. If you do not wish to reload, then you will not be able to do certain Umpani missions.