The object of type "PlaymakerFSM" has been destroyed but you are still trying to access it.
I have 2 levels i load in the very same way, in one event i can toggle between the 2 levels with no errors or issues, on the other i can load the main level but when i click the button that loads the next scene it transitions but then sits there with this error msg.
Ive tried changing how to load the scene a couple of time (many couple of times) and the issue arises everytime i add a PlaymakerFSM to the scene, without it the lvl loads fine with no issues so each time i remove the FSM the level loads, add an FSM and its a bust.
It weird that the other scene does not have this issue at all. Ive read upon all the other MissingReferenceExceptions and nothing really helps, i am using version 1.3.2.