If you Google Prime95 Wiki you'll come up a list of Updates on the Prime95 Program.
I believe it is:
27.6 beta April 24, 2012 Bug fixes; (v27.5 was skipped; the underlying math libraries went through a revision, but Prime95 was not modified.)
I'm on a work computer atm, that wont let me view the bug fix info. But there's one that states: does not work on Bulldozer CPU.
If you google Prime95 the top downloads are version 25.11, which it's possible many people were running this version and having issues (user error - due to older version)
Given proper cooling and working overclock settings I haven't noticed Prime95 fail when another program was able to pass (IBT-10 pass Maximum, OCCT, AOD)
I didn't notice if the OP managed to get a working overclock on their CPU. I wrote an Asus guide for these CPU's (in my Sig). Feel free to check it out. Hopefully it can bring some insight to overclocking on your ASRock board, if things are similar.