How to remove an image from a window?

[DerVVulfman]

Maybe you should try this...
Replace:

Code:

@Map.dispose

with

Code:

@Map.dispose unless @Map == nil

which only disposes @Map if it still exists.

Now replace:

Code:

if Input.trigger?(Input::B)
      $game_system.se_play($data_system.cancel_se)
      $scene = Scene_Map.new
    end

Code:

if Input.trigger?(Input::B)
      $game_system.se_play($data_system.cancel_se)
      @Map.dispose unless @Map == nil
      @Map = nil
      $scene = Scene_Map.new
    end

Which can delete/dispose of @map on the keypress. After that, I set it to 'nil' so IF it is disposed this way, the system won't try to dispose it again at the end of the main routine.