I ran FIND DUPLICATES from the toolbox for the first time ever a couple days ago. Computer was working fine, I closed all apps and ran FIND DUPLICATES. It rant for about 35 minutes. When the list came up of duplicates, I delete one file and then quit the app as I had to go to a meeting. At that point, all hell had broken loose. I could no longer log into my Apple Account in System Preferences, but could still log in to iCloud.com. All my emails and calendar appointments were gone. There were still on my iPhone and iPad - just not on the Mackbook Pro. Then I discovered over 1,200 files in m,y Dropbox had been deleted. Luckily Dropbox has a restore deleted files in the past 180 days so I got them back. All my apps that require licensed and require user name and password when you install them (MS Office, all my Adobe apps, etcs) have to be re-authenticated again. Luckily I have AppleCare on the Macbook and I was on the phone with tech support for 2.5 hours Friday. We did screen sharing and they downloaded diagnostic tools and I ran them and ent them a 300MB+ result files, screen shots and scren recordings and they are still stumped on why I can't log into my Apple Account in System Preferences - which of course is what is screwing up email and calendars. All this happened IMMEDIATELY after running FIND DUPLICATES. I have deleted it from my Macbook and will never run it again. I can't prove that FIND DUPLICATES did this, but all the evidence points to it.