empty space

I´m using El Capitan on a MacBook Pro (late 2011). I have a 27Gb empty space partition that I just can´t erase. I want this partition to be merged with my HD.

However, when I try to erase it, the Disk Utility shows an error message saying that the directory items count is invalid (should be 72714 instead of 72716) and that the Macintosh HD is corrupted and needs to be repaired. I already repaired it (7 times to be true...), but the problem persists. Does anyone know what should I do to solve this?????