Ren'Py Fantasy GUI Kit

Hello, I'm running into an odd exception while trying to open the test game. It won't launch and gives me this exception:

  File "C:\Renpy\renpy-8.0.3-sdk\renpy\bootstrap.py", line 277, in bootstrap
    renpy.main.main()
  File "C:\Renpy\renpy-8.0.3-sdk\renpy\main.py", line 558, in main
    renpy.game.context().run(node)
  File "game/gui.rpy", line 15, in script
    define config.check_conflicting_properties = True
  File "/home/tom/ab/renpy-build/tmp/install.linux-x86_64/lib/python3.9/site-packages/future/utils/__init__.py", line 441, in raise_
  File "game/gui.rpy", line 15, in script
    define config.check_conflicting_properties = True
  File "C:\Renpy\renpy-8.0.3-sdk\renpy\ast.py", line 2441, in execute
    self.set()
  File "C:\Renpy\renpy-8.0.3-sdk\renpy\ast.py", line 2459, in set
    ns.set(self.varname, value)
  File "renpy/common/000namespaces.rpy", line 33, in set
    setattr(self.nso, name, value)
  File "C:\Renpy\renpy-8.0.3-sdk\renpy\defaultstore.py", line 105, in __setattr__
    raise Exception('config.%s is not a known configuration variable.' % (name))
Exception: config.check_conflicting_properties is not a known configuration variable.

I'm not the best at GUI coding, so I'm a bit stumped. How might I go about fixing this?