I think this was the case for one version of King's Bounty: The Legend on GOG (not the current version it sounds like?), which had a bug where you couldn't talk to an NPC at one point when you needed to do so to advance the game. At least, I recall someone mentioning somewhere when I looked after encountering the bug years ago that this was an issue of a random crack posted to the net that someone (the publisher I'm guessing, maybe GOG or the developer) had applied to produce the GOG version.