map2dif is an exporter. It doesn't have any interface at all. Basically, when you start it up, you're telling it to do the set of instructions you sent to it. Since you haven't given it any instructions, it just closes. There are two ways to get it to do what you want:
a. Get a program like Quark or Torque Constructor to do it for you. This is easy and highly recommended.
b. Use the command prompt. There are instructions on how to do this
here.
You shouldn't be opening the mission editor. Here is how you start it.
1. Find blockland.exe.
2. Right click it and select "Create shortcut"
3. Right click the shortcut, and select properties.
4. Go to the field that says target. Click inside of it, press the end key, and type -mod editor
It should now look like this:
"C:\Program Files\Blockland\blockland.exe" -mod editor
5. Click okay.
6. Start the game using the shortcut.
7. Open a mission.
8. Press F11.
