I did the tut for locakable doors and got a CTD with this message when I tried to open the door before unlocking it. The only other thing related that I found was for an elevator.
Try rebuilding the door. Is your trigger going through the door or 2 seperate ones. if you have 1 going through the door it may cause an entity leak. How did you script it.
BTW for your multiple objectives question look at the m2|1 level script and it shows how to do multiple objectives.
