Your startup disk is almost full

The drive is full and you must delete data or move it to the external drive

Open Finder, select Macintosh HD under Devices and hit Space key to check what free space you have on the drive

I had this problem and the cause was Mail. It kept trying to recover a message over and over. I googled it found the resolution.

I remembered trying to send a really large video file that would not send. Mail kept trying to recover that e-mail. After I removed that e-mail from mail and the file system I gained about 80GB.

I will try to find the instructions on fixing the mail problem.

Try to go here and read about the mailbox being full:

https://discussions.apple.com/thread/3879044?start=0&tstart=0

Or serach for:

User Library folder has 112 GB...something must be wrong!

This is basically how I fixed my problem.

It may or may not be related to Mail - do you have a lot of videos, music, or photos, they are huge files, so could be part of the problem.

Your hard drive has a certain amount of space and you should have an absolute minimum of at least 10 - 15 GB free/empty at all times for the OS to operate properly. So, check to see what files are hogging the hard drive space and either delete them or move them to an external drive so you can delete them on the internal and gain some space.

You'll also need to delete the files from Trash, otherwise they are just moved there and still take up disk space.

You do realize this thread has been dormant for about a year?

It means that there is not enough space on your hard drive. You have to delete some large files to release more space on your disk. I personally love CleanMyMac. Refer to the article below: http://hexinpeter.com/wordpress/cleanmymac-2-macpaw-promotion-half-price/