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Not a failing hard drive! Actually, it might be - I have no way of knowing for sure, but I've been told this by Apple Care but it wasn't the case... TWICE. I'm on MacOS Sierra version 10.12.6. Try clearing cache files first - seriously! Go > Go to > /var/folders > find any folders except for zz (should be a couple or a few folders besides zz, such as l7, 0b, etc.) > then go into the folders until you get to the O, C, and T folders and clear them. Then empty your recycle bin and restart. You should see your app icons again and be able to open them.
[doublepost=1532441461][/doublepost]I’m having this problem also on a Mac Pro 10.13.6. Finally found the files, deleted them, and all is good. Thank you for this informational site.
 
Not a failing hard drive! Actually, it might be - I have no way of knowing for sure, but I've been told this by Apple Care but it wasn't the case... TWICE. I'm on MacOS Sierra version 10.12.6. Try clearing cache files first - seriously! Go > Go to > /var/folders > find any folders except for zz (should be a couple or a few folders besides zz, such as l7, 0b, etc.) > then go into the folders until you get to the O, C, and T folders and clear them. Then empty your recycle bin and restart. You should see your app icons again and be able to open them.

I moved those folders (other than zz) and it solved my problem. Unfortunately I failed to empty my Trash until after rebooting. That left some of those items that were dragged to Trash being used by some processes, so they can't be removed from Trash.
 
I moved those folders (other than zz) and it solved my problem. Unfortunately I failed to empty my Trash until after rebooting. That left some of those items that were dragged to Trash being used by some processes, so they can't be removed from Trash.

I wonder if you are able to restore those files from the Trash and then delete again, and this time empty the Trash before your reboot. At any rate, sounds like your apps are up and running again, so that's good news.
 
Hi, I wanted to chime in with my experience. Suddenly got this error, was freaking out because I could open /var/folders but could not delete any of the non-“zz” folders as the OS wouldn’t let me. What I did was, open the non-“zz” folders, look for the folders named O T or C. I deleted anything I could delete from those folders, anything the OS would let me delete, and now things seem to be okay (after a reboot).
 
Hi, I wanted to chime in with my experience. Suddenly got this error, was freaking out because I could open /var/folders but could not delete any of the non-“zz” folders as the OS wouldn’t let me. What I did was, open the non-“zz” folders, look for the folders named O T or C. I deleted anything I could delete from those folders, anything the OS would let me delete, and now things seem to be okay (after a reboot).

You figured it out - you have to clear the folders of content rather than delete them. Anyhow, glad it worked!
 
I literally just made an account on this forum to thank you because it worked!!! I have a late 2011 MacBook pro, last week updated to High Sierra and this morning I woke up to all my app icons replaced with question marks, and pretty much all files either “damaged or incomplete”.
Clearing those cache files worked perfectly! Thank you :D
[doublepost=1560681396][/doublepost]Thank you millions, this worked June 2019 and still happening whatever it was or is
 
Thank you a lot jpete! This has also saved my day and my week probably. Very surprising that this cache story can have so dramatic effects.
Thank again
 
I installed the macOS 10.14.6 update this morning and ran into this same problem. This solution worked for me too. I have to admit I was skeptical, but I deleted one folder from /var/folders (not zz) and now my Mac is back to normal. Amazing.
 
I am experiencing the same problem when trying to open Excel. I have 2x deleted everything in the O/C/T folders by moving them into trash. Then I cleared my trash. When clearing trash I get notifications that many items cannot be deleted. Then, after re-starting, most files have returned to the O/C/T folders. Sort of frustrating and very creepy! Any ideas?
 
I am experiencing the same problem when trying to open Excel. I have 2x deleted everything in the O/C/T folders by moving them into trash. Then I cleared my trash. When clearing trash I get notifications that many items cannot be deleted. Then, after re-starting, most files have returned to the O/C/T folders. Sort of frustrating and very creepy! Any ideas?
You could always try deleting with
sudo rm <pathToFile>
You can drag the file into Terminal to fill in the path
 
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