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Well, generally, the folder with maps should be located in the game folder, and the path to it should only contain folders with Latin characters. The map itself should also be named using only Latin characters (I'm not sure about numbers, but I think they are allowed too). Is everything set up like that for you?
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Reinstalling usually helps, but make sure you're installing it in the correct location.
What's strange is that I have the original game and two expansions here. Before I started playing the campaign, everything worked fine. Now, after completing the original game, Hammers of Fate, and half of Tribes of the East, the editor started acting up.