Says error while updating core files but I can continue past that then it says let's me into the black screen login area. But when I type my login and username it says successful logged in then says closing out and screen go away. Any help? Thank you

I'm going to assume you're talking about the Ashita2 launcher since you didn't specify. A couple weeks ago(literally just 2) there was an Ashita update that borked connectivity. A quick DL and reinstall should fix it.