I filed a question two days ago with support after Giants: Citizen Kabuto started crashing on launch after changing video cards. I just got a response back for that topic:
"Please try to reinstall game - Giants install diffrent graphic libraries for diffrent graphic cards. Game should work after reinstallation."
Except this was the first thing I tried, and I mention in my message that I have already tried this. "I've uninstalled and reinstalled the game since switching video cards with no effect."
Is there no way to respond to the thread of questions on gog support?

did you delete everything? Simple re installation may not help since some config files can be left. delete whole folder and any other used by the game.

This fixed the game, thanks!
The email address that was sent from is generic "Support@gog.com", though.

It's not a problem, you can send your mails to support@gog.com, don't worry.

I was actually very impressed with that, the way it automatically connects your email like that. :D