X2 555 unlocked to X4 B55 @ 3.8GHz
Oh, and its from batch 1009CPMW and on an MSI 785GTM-E45
Hmm. I had a 555 BE on an MSI 785GTM-E45, and every time I enabled the "Core Unlocker" feature, whether or not I enabled ACC, it simply wouldn't boot.
I figured unlocking was bust on that board.
On the other hand, I had a 720 BE on a Gigabyte 785GM-US2H, and when I changed "EC FIRMWARE" to "Hybrid", and enabled ACC "Auto, all cores", it unlocked like a charm. It also displayed a message about flashing the EC Hybrid firmware when I saved and exited the CMOS. The MSI displayed no such message, which is why I think it didn't work.
Does your MSI board have a setting for "EC Firmware"? I couldn't find one on mine.
Also, did you update the BIOS? There were no updated BIOSes listed on their web site, but only links to their "Live Update", both options which didn't work.