Rxo

Hey mate, your model has n-gons, like your error is trying to tell you. N-gons are planes that have more than 4 vertex points. So you need to get rid of them. Game Engines can't handle them, and the arma tool which you are using to export things for arma is checking if you have any. The quick way is to triangulate everything or search with a blender tool for planes with more than 4 vertex points.