Jack_of_shadows
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In the game, the map might not display for other reasons as well. As far as I remember, it should meet a number of minimum requirements for this to happen (at least two players, possibly some other conditions). As for the fact that it doesn't open in the editor, I can only assume that it was corrupted during the previous save. For testing, you can try opening other people's maps, creating some of your own, and checking the statistics. If it always fails to open, it's best to reinstall the game.