Every time I try to submit a Brawl deck with the card "Karn, Living Legacy" as the commander, I get an error, and can't submit the deck. I replaced the commander of the deck with another legendary creature, changed nothing, and the deck saved properly. After going back to the deck to edit it, and trying to replace the commander with Karn (changing nothing else), I once again got an error.

Please fix this so that I can make a brawl deck with Karn, Living Legacy as the commander