So Steam updated itself a while back. I have been meaning to get to this but here is a walkthrough on how to fix your game so you can still play it in Steam.

The user [IG] Archivist posted a "working" solution in another discussion:
1. Launch Steam app as usual
2. Delete/rename the file GameOverlayRenderer.dll/GameOverlayRenderer64.dll from the Steam root folder
3. Launch KAG/KIS
The files are related to the SHIFT+TAB overlay screen. WIth that function out of the contest, the game seems working (for some people, at least). Tested it and it works!

That was the only way I got KAG to work again.