[Resolved]Window_Base Error

It's from an unofficial demo of Project Leviathan
Right, so the weird thing is when I play it no such error appears but when HowlingWinds plays it this error pops up.

Here's the section of the Window_Base script :

Spoiler for:

Code: [Select]

#--------------------------------------------------------------------------
  # * Create Window Contents
  #--------------------------------------------------------------------------
  def create_contents
    self.contents.dispose
    self.contents = Bitmap.new(width - 32, height - 32)
  end

Line 54 is " self.contents = Bitmap.new(width - 32, height - 32)"

EDIT:Never mind, it seems that it was because the font wasn't installed yet. >_<