If ShuffleIT want to hotfix this issue then the error message needs to be more helpful. It currently tells you there's a problem, but doesn't really pinpoint what exactly is causing the issue not help the user rectify it. If familiar cards are causing the issue it should say something like:
"Could not create a game with at least 10 kingdom cards. The combined Familiar Cards settings of all players does not allow enough cards. Please either disable the "Respect Familiar Cards" table setting, or ensure each player has configured their familiar cards appropriately."
Alternatively, don't show a message at all, and just have the game automatically disable the option and try again, and in the created game, post a message in the chat box that says "The Respect Familiar Cards setting has been disabled for this game as not enough cards were available."