For a quick description of this bug, it works like this…
The game boots up correctly, as in it does not crash. The main menu screen with Mew appears, and the keys all seem to work. You boot into the New Game/Save File screen, and when you select either, the game goes to a black screen. Music plays in the background, but nothing actually appears on screen. The game either crashes or you are forced to use Task Manager to close it.
So, it really is as simple as the Core/Patch you got off of the Forums is a bad download. Something about this download causes issues when using any browser to download (I tested both Firefox and Chrome - Still trying to test Edge/IE).
So what you do is simple, although it is annoying. You need to wait around 3-5 hours and try again. It probably has something to do with server traffic that such a large file has an issue downloading correctly.
Anyway, the best thing to do is to download at the times when the least amount of people are on, as in Midday (11am-1pm) or extra late (11pm-1am).
A good indicator if your download is a clean download is how much time it takes. Bad downloads took me around 3-4 minutes, whereas my clean download took me 9 minutes. Now this time can vary a lot depending on many factors, but a good indicator of a clean download is if the time in the browser is much more than your last failed download.
As of right now I do not know of any better way to tell if your download is clean or not before attempting to boot it up, but that is all we have right now until we find out more about the problem.
Hope I helped!
A Quick edit- My current properties for Game.exe are Compatibility XP Service Pack 3 and "Run this Program as Administrator, as well as adding it to the Data Execution Prevention - directions here