Ive upgraded my forums from 3.8.4 to 4.0.6 tonight and had aload of problems since, (see this topic) and ive got the main problems nailed now i think.
Last one i can find is in the admin cp, its returning a page not found error everytime i do something, it will carry the action out but then give me a page not found page instead of taking me back to the admin cp, asif the auto redirect is not working?