Apple MacBook Air mid-2012
There is some "corruption" on some of your files.  Since you already ran the Disk Utility and it came back clean it is telling you that there are no physical errors with your drive.  That's the good part.

You have a couple of options:


Run fsck
Do a clean install


Running fsck.  You will need to do so in single user mode (hold down Command-S during boot)

You will know that this worked because you will see a black background with a ton of white text scroll down your screen.

When you are done booting, you will see a command line prompt.  Enter the following command:

#fsck -fy


(Don't enter the hash tag)

It will complete and tell you that the file system was modified.  Keep running the above command until it tells you that the volume is "Ok."

When you are done reboot the computer by issuing the command

#reboot


Your MBP Air will reboot normally the error should go away.

If it dosen't it is time to do a fresh clean install.  

There are third party utilities that "may" work here, but I have found they cause more problems than they are worth.

Oh...most important part:

Make sure you have a backup of all your data!!!!