I just downloaded Ag Skies 2 from the Curse client, loaded it up all fine, tried to login, and get "A fatal error has occured." and nothing else. Any ideas?
Problem resolved. For archive purposes: Using MultiMC Launcher, Create new instance, Download the ALTERNATE zip file from the Agrarian Skies 2 curse page(roughly 270mb), click Edit Instance on the instance you just created, Install latest recommended Forge version, and then extract the files from the Zip, into the minecraft folder of your selected instance.