2002 happens a lot when you have poor internet connection or your internet credentials change (blame windows for that).
you could try resetting your internet connection settings by Network Reset, this will make you reset your pc to take effect but will make you have to reconnect to the internet again, such as your wifi and password to it.
there is no real fix for these unless square enix adds a feature to repair connections to server. while they are at it a file checker and game repair would be really helpful to the player spending 18 hours re-downloading the game