I also get this problem when saving to a normal disk. Mac OS 10.13.3

I work with files saved to Google Drive and I get this message in Illustrator — not every time I go to save, but quite frequently.
When it does happen, the file has definitely not been modified outside of Illustrator.
I work with files on my hard drive and synch to Google Drive: I had assumed that perhaps I get the message when the synching is in progress?

Been happening ever since the upgrade to 10.13.3. Also I have to keep resetting Photoshop files to popen with Photoshop. Daily issue for both.

I've been getting the same message in various files, for a week or two.

I recently upgraded OS to 10.13.2, but that was over a month ago, so not clear it correlates to OS update.

It also seems to be random or intermittent - I only ********* certain files, and sometimes I DO NOT get that same message on same files!

And no, the file was not edited online or on a different computer, etc.

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

Same issue as everyone else... Not saving to dropbox, no external drives. Everything stored locally... Hope a fix is determined soon...

I too started getting this after High Sierra and CC updates. Working locally, iMac 10.13.3, not using Fonts. It happens every time I manually save, and every time it auto-saves.

I am having the same issue. On files going to iCloud, Dropbox and files only on my Hard Drive. I do not have iCloud Drive set to backup all files. No matter if the images are embedded or linked, and layers locked or unlocked. Everything I save with Illustrator issues a warning of modified outside of illustrator. I created a test file with only linked and embedded images from my hard drive with the same result.

I find if you lock all your layers before saving it's fine :)

Started happening to me just today after updating to 10.13 His Sierra. According to this thread this has been going on since November?!

This error was a normal part of my routine about a couple of years ago. I remember it had something to do with a version of Suitcase. Illustrator was sensing that Suitcase had modified the file (fonts)? In my experience, this does not occur in a file that does not contain type.

It only happened to me when I opened an Illustrator file with an embedded jpeg. It didn't happen with a linked jpeg.

After updating to Siera, Illustrator CS5.1 keeps crashing every time i try to use fonts. I also get the same message "this file has been modified outside illustrator" when i try to save my work. I can't even preview fonts in the font panel. Adobe has stopped updating older software regardless if you paid $1500 for the creative suite because they want to force people to buy their subscription service.

I think the Adobe company has turned into a awful greedy company that cares more about their shareholders than their actual products and customers. I'm a graphics designer, photographer and web designer that works with 10 other artists and we' ll make sure to let everyone know how horrible this company has become. No more Adobe.

I am getting this too, just updated to High Sierra. I am a production artist, this issue is IMPORTANT.

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?