Duck and Cover

i got a special encounter, but it said something about not having the mission file :

it happen again... now it said fail to load blah blah blah

I think the Pipboy encounter is the last special encounter that you can come across. Since there are no more special encounters for the game to load it gives the error message and quits(I assume because it has happened to me). So my advice is just to skip any more SE squares that you might come across during your game.

Either that, or just avoid the squares all together, the squares stay the same. If a SE is in one square, that square is a SE square, it will always have a SE in it.

Unless you happened to start out trying to hit 3 or 4 SE's in a square. Then you will run out of SE's before you hit all of the potential locations.