Custom entities in custom story, "file index out of bounds"

[GraphicsKid]

Hi, I have a custom entity in my map (just the prison door, but a mover so the player has to use a lever to control it). It works perfectly in game, but every time I start up the editor, I get this message: "Found some errors while loading file. Check log for details. File index out of bounds!". Lo and behold, the door is missing.

I don't know what log file it's talking about anyways...

EDIT: Stupid me, forgot to mention the most important part: These custom entities reside in a subfolder "entities" in the custom story folder of my custom story. (so \custom_stories\my_mod\entities)