Current questions and answers regarding the map editor.

I've read many pages, but I still haven't found an answer to my problem: I'm creating a map, but when I save it, it weighs 22 bytes. I check for errors, and it says that the map is "satisfactory," but then when I save it, it displays a message: "Since you have modified this map, the rmg marker will be lost, and multiplayer regeneration will not work." What should I do? Please tell me how to create a map correctly so that it works, step by step.