I also had this problem with my setup, trifire 5770 and 11.7 upgrading from 11.6. My crossfire wasn't able to be activated and it said that my other 2 cards were disabled even though device manager and msi afterburner both saw the cards. GPU-Z also said no Xfire.
Using the guide that Aaranu posted on page 1, post 3 I believe
BradleyW's guide to uninstalling ATI drivers
This worked for me, didn't have to fresh install.
I also shut down and reseated the 2 crossfire bridges, that probably did nothing but it made me feel better.