I had a similar problem with my macbook. Try getting Onyx, because that's what i did and it told me to reboot and press some keys and access disk utility from there, and do the same repair disk thingy and that's when it worked! 🙂
Sorry cant remember what you have to press when u reboot ! 😕
EDIT: When you reboot hold Command + R, which will take you into Lion recovery disk assistant or something and access disk utility from there to repair your disk