This means that your first map transition cannot be from Whole Map.
You must specify a door, like Wolf 359 in the Sirius sector or one of the sub-basement doors on ESD, etc.
Does that help? You select this door on the map transfer widget in the story editor.
Yes, that helped... I might suggest making that clearer in the error message list... put that little yellow warning symbol next to "whole map". Clicking the error just made it scroll to the Kill Encounter, which wasn't where the problem is.
It's a bit moot, since I get "Save failed!" when trying to save my mission now.
Do my eyes deceive me.... or can a potted plant in ESD be made into a door?