This isn't so much help as a bump, but welcome to LQ and hopefully somebody can help you out soon.
The rivafb thing is just a generic warning, I believe. I got the same message. Try 'lsmod' and if you had it, I'd think it would show, but you probably don't. 'rmmod' would be what you wanted if you did. You could check that out anyway and see if anything else looks wrong. Maybe post the output of 'lsmod' here and someone could see something amiss. Also check out /var/log/X*.log and see if its (WW) or (EE) has anything interesting.
No idea about the dual-head, sorry. There's an article on that at the LQWiki
that might help.