OH MY GOD!
I now know what the bug is. It was because of the Jenga mod where I moved MA R'lyeh into early age to give it coastal recruits. That's why llamaserver is throwing fits, because it thinks that you are basically sending MA prentenders into early era game. I don't know why it accepted R'lyehs pretender in the first game, but it was likely the cause of error.
I'll just make the game "multi-age" game, so that the game accepts pretenders from all eras. That should fix it. Just be certain that you have the Jenga mod enabled when making pretenders.
So yeah, my bad. Please feel free to verbally mock me if you feel like it, I deserve it for not figuring this out sooner.