Quick question - have you tried to absolutely clear your browser from cookies and cache, have you tried to turn off your server and restart it completely after upgrade? I know it's not much but i've seen some people get rid of login error after they clear browser cache or server restart. Since it's so trivial task i suggest you do it.
Quick question - have you tried to absolutely clear your browser from cookies and cache, have you tried to turn off your server and restart it completely?
I am very sorry i almost feel your pain. Let us know when you (or support) solve it. I am genuinely interested to know what caused it and how you dealt with it.