Unfortunately I forgot to disable the "Save" and "Load" buttons because they are not functional at this point. For build 5 I added an auto save system, which will allow you to load back to the last checkpoint. Also I have a quick save system from build 4, which can be used by pressing "F5" to save, and "F6" to load instantly; the quick save system in build 4 wasn't fully working, but now I think I got it.
I made some changes that should make the game run better, and additionally added an in game graphics menu under "Options" that can allow you to tweak the game performance.