Quote Originally Posted by diddi35 View Post
Worked fine for me too until I switched from X2 550 (c2) to X2 555 (c3) booth unlocked to X4. Maybe some kind of issue related to C3 Stepping
Improvements introduced with the C3 revision:

# Hardware C1E implemented: Faster switching of power states means virtually no impact to performance by power management when BIOS support is properly implemented. (From here: Link)

Did you tried to clear your CMOS data and then load setup default (and reboot) before you start tweaking/unlocking/etc?