I understand (being in IT myself) the amount of work involved in an upgrade like this but I would consider this an epic FAIL, to the point you should be restoring the old forum. I get 3 different issues on 3 different browsers all trying to do the same thing. The main problem is how your embedding the new forum into the old rcuniverse header and menu and old control panel. The logins are not working and the browser is not keeping you logged in when you move from page to page.
I've managed to post this by hitting refresh on the page in Chrome about 10 times until it thought I was logged in.