Sometimes anti-viruses take parts of RenPy engine (the one we use) as a virus for god knows what reason, same as it happens with .exe files for some games. It is safe to download, otherwise you'd see a lot more complains in the comment section.
Regarding your problem on Gamecore, sadly we won't be able to help, because that seems to be the problem on their end, and since we don't officially support that version, we have no way of fixing it. You can try and contact their support, but that's all I can suggest in this situation :(