It seems that you're using an outdated browser. Some things may not work as they should (or don't work at all).
We suggest you upgrade newer and better browser like: Chrome, Firefox, Internet Explorer or Opera

The game won't start, this message instantly pops up, and that's it. I looked around for solutions, and I saw installing XNA may do the trick, so I attempted to do that, and it said I needed Visual Studio. So I followed the link in the installer to a 6gb installer, yet XNA gave me the exact same message.

I've probably been 2 hours trying to get this game to work, and I'm very tempted to just refund it. I haven't run into problems like this for probably 15 years, and there is really no excuse for it these days as it seems to be a common issue with this game.
OK, got it fixed.

I contacted the dev's directly through their website, and was told the GOG version may have a modified installer. That prompted me to try the demo, and straight away, it installed the correct versions of XNA and .NET, which fixed the full game. The GOG installer never asked, and doesn't include the installers in the games folder.

Anyway, the dev support was solid, and gave me a few other solutions, which I'm sure would have worked as well. It seems GOG is the one to blame here though, and really needs to fix the games installer to include these required elements.