I'm getting this error too:
Mac OS X 10.13.2 (17C205), Illustrator 22.0.1.

I am also having this issue after upgrading to OS 10.13 (High Sierra). I am on Illustrator 20.0.1 and am saving my files to the local drive.

I save my files multiple times throughout working on them, but the error only shows up every couple of saves. During this time the file will be open in Illustrator, not being used by any other programs (that I know of). Sometimes I will need to switch to the login screen while away from my desk, but that is the closest I get to actually "closing" the files the whole time I'm working on them.

I'm having this issue as well. My files are stored, edited, and saved on my local drive.

Have been getting this error as well. 10.13.2, Latest Illustrator 22.0.1. I AM NOT storing the affected files in Dropbox. They are on my local internal hard drive. I do use Dropbox but again, none of the files that have given me this error are in my Dropbox.

I recently had to upgrade my computer because the virus protection would not work any more. SO I bought a new MAC with the High Sierra 10.13.3 operations system. The techs thought I would not have a problem with my older CS5.1 Adobe Software. WRONG!!! I can't open or save or save as with Illustrator which I totally really on to compose logos and artwork. I can use Photoshop and InDesign, but when I quit them I get error comments. I can't afford to pay by the month...I already paid plenty over the years for the software I have now. I am so ****** off!!! Any solutions? I tried the JAVA upload and it did not work. Any other software compatible with MACS that is identical to Illustrator and can use the files I already created?

I recently had to upgrade my computer because the virus protection would not work any more. SO I bought a new MAC with the High Sierra 10.13.3 operations system. The techs thought I would not have a problem with my older CS5.1 Adobe Software. WRONG!!! I can't open or save or save as with Illustrator which I totally really on to compose logos and artwork. I can use Photoshop and InDesign, but when I quit them I get error comments. I can't afford to pay by the month...I already paid plenty over the years for the software I have now. I am so ****** off!!! Any solutions? I tried the JAVA upload and it did not work. Any other software compatible with MACS that is identical to Illustrator and can use the files I already created?

I am getting this issue when I am saving to a Google Drive linked folder. Adobe CC latest version.

Issue occurring here as well since High Sierra update, on multiple iMacs. Files being worked on are local (saved to a variety of folders such as Desktop and Documents) and dropbox is not in use, nor are iCloud Drive or Google Drive. One of the iMacs in question has been upgraded multiple times as new OS updates are available, while the other recently had a hard drive replacement and was set up fresh with new installs of all CC apps.
Any updates from the Illustrator team on if this has been successfully reproduced and is being worked on would be much appreciated.

Also it's happening even with files that are not (and haven't ever) been saved to Dropbox. Files just saved in my Documents folder.

I am having this issue as well after upgrading to High Sierra.

Are you guys working on fixing this? Obviously, a large number of users are experiencing it. High Sierra is at fault. I have 2 iMacs, and neither were affected by this problem until the upgrade.

I get this popup every time I save to a location that is synced with Dropbox.

This popup never appeared in previous versions of Illustrator.

Do yourself a favor and drop Adobe software. At my graphics design company we switched to Affinity Designer and Affinity Photo a year ago and we love it. A one time fee and no monthly payments. The idea that you need to use Adobe software to be a PRO, is ridiculous. Affinity products are for PROs.

This bug should be a priority if you consider Illustrator professional software.

Professionals use cloud and sync services. Professionals use backup services. If you keep treating Illustrator like a hobby, professionals will use other software.

I started receiving this same message today I just started a new Illustrator file and an hour into my illustration it started appearing. I only have this file saved on the desktop. I'm running the latest Mac OS.

Funny thing is: Photoshop and InDesign do not produce this error message (running latest CC versions and macOS 10.13.3). So there seems to be an Illustrator-specific way of checking the timestamp or permissions on APFS.

I started receiving this error once updating to high sierra. I've noticed it happening when saving to my local creative cloud folder as well as my external SSD hard drive. It happens even when I don't edit the file on a separate computer but after I make changes and save numerous times within one sitting.

After playing with it a bit more, I think I might have gotten it to stop.
I Save As>replaced the file with same name>As Illustrator...but I made sure in the Illustrator Options window under optionsCreate PDF Compatible File was checked...nothing else was checked.
I noticed before that Use Compression had been checked and Embed ICC Profiles had been checked....so I save with them un-checked.
Seems to be working fine now.

I am getting the same message and I am not working from a separate sever... the files are on my hard drive – even on my desktop.
Seems that I can alter once, Save... no problem. Alter a second time, Save.... message starts. No matter what is done. Even went as simple as Open, click on object, move with down arrow once, Save....OK; Click object a second time, move with down arrow once, Save.... message comes up.
Very frustrating.

same issue, never had this show up before. macOS high sierra 10.13.2, iMac 27" , 32GB, NVIDIA GeForce GTX 780M 4 GB. Files are inside drop box folder, but that was never an issue, used to work perfectly.