Error Code 3 From Launcher

I keep getting an error trying to connect to Diablo 3 through the Battle.net launcher: "There was a problem initializing the party state. If this problem persists, log out and log back in. (Code 3)

I’ve logged out of the launcher repeatedly and re-authenticated, rebooted but still am having this same error. WoW Classic loads fine from the same launcher. Just started today.