This quest is missing properties (the error is only from one missing property, but others are missing too).
In addition, there have been left over properties that are no longer used by the script (the sort of stuff that throws 'property cannot be initialized because the script no longer contains that property' errors).
One of three fog condenser refs is apparently not existing in the game (it wasn't found by AutoFill). Left this at 'none' because the quest script is not using it anyway.
Because one of the missing properties was the CompanionMurder_MacCready form list (this is the one that threw the error), and the quest was supposed to add stuff to that list, a retro script will be needed to make sure that this stuff is added if the quest has completed running already.