I've put my custom entity in the redist/entities folder. And after that the LevelEditor finally found my entity.
No report called: "Found some errors while loading file. Check log for details. File index out of bounds!" Mudbill
But that makes me very curious what would be happen when my custom entity stay only in my custom story folder.
In several tests, I found out:
Of course, the LevelEditor can't find my entity anymore. Because the LevelEditor was programmed to grab datas in given folders in redist. But not in custom_stories folder.
But Amnesia: The Dark Descent seems to be a fuck about that. That game doesn't matter what the LevelEditor was looking around.
Because that game was programmed to grab datas almost in total area.
Finally I put my entity in the redist folder if I'm working on the LevelEditor. And I'm thank you both for the quick report. I have pondered by this problem. Very long time.