I am a new Mac user, I have the Black Macbook, and I just encountered the same errors with Onyx. Thanks to Brown Study's I booted the system holding down Cmd S.
then typed in fsck -fy Including the space.
and it went throught some repair action there for a couple of minutes. I booted back and ran Disk Utility and all is well no more errors. Disk Utility did show error before this little stunt. and Now NO ERRORS