Gydion: Earlier GOG thread
about this. It even has the same link. Took me a while to find it though.
This thread should probably be pinned by GOG, since it seems like it's a problem that's affecting more people lately (including me), and is specifically related to older games.
The problem with this fix is that it will fix problems with older games, but will simultaneously cause problems with newer games. You will get a new error message that says "Failed to create the GameExplorer object."
The original version of Bioshock is an example of a game that will not launch when this fix is applied.