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

I purchased and installed the game as soon as it was available on GOG, and do not think I have updated it since then (I can't remember, and I have no idea how to see the version number).

Trying to install the 1,2GB patch to 2.01 (GOG-4), however, I am simply told:

"This patch does not support your version of the game please download a new installer"

The installer also says it's "Update", not 2.01 as GOG tells me in the download section.

So what gives? As it is, I'm just simply uninstalling and reinstalling the whole goddamn thing. It's only 0.5GB bigger than the patch. But I'm still curious as to what is at fault here.