I had this problem once too. The thing that fixed it for me was giving a texture to my maplet model. For some reason, if it did not have a texture, maplet would export a blank document (with no triangles, vertecies, or anything else). If you already have a texture applied in maplet, I don't know what is wrong. If you don't, try the Texture-Replace button in Maplet.
Hope I helped you a little.
Hope I helped you a little.