Using a memory card to configure my me p2p tunnel the chat displays "Invalid Machine".
I'm playing in a singleplayer world.
I've tried to clear it, restart the game and stuff like this but it continues doing like this.

• Minecraft Version: 1.12.2
• AE2 Version: rv6-stable-7
• Forge Version: 14.23.5.2847

I would guess your are holding something in your offhand. If so, that is simply a forge we cannot fix on our side.

Maybe it did like so because I had baubles on or stuff like that.
I've tried without any of that stuff on and it worked!