Holy cow, I just upgraded to High Sierra and immediately discovered the same problem as everyone else with Illustrator (CC 21.1.0) and Dropbox(v39.4.49). I save to a folder on my hard drive, which is synced to Dropbox. After that file has been synced to Dropbox, something mysterious happens and Illustrator thinks the file has been altered (name change, or something?) outside of the application. So, when trying to save that file again from within the application, the message pops up. Only happens with Illustrator, and started happening immediately after upgrading to High Sierra (10.13.1) Been working in this same manner for a couple years with no issues until now.
Holy cow, I just upgraded to High Sierra and immediately discovered the same problem as everyone else with Illustrator (CC 21.1.0) and Dropbox(v39.4.49). I save to a folder on my hard drive, which is synced to Dropbox. After that file has been synced to Dropbox, something mysterious happens and Illustrator thinks the file has been altered (name change, or something?) outside of the application. So, when trying to save that file again from within the application, the message pops up. Only happens with Illustrator, and started happening immediately after upgrading to High Sierra (10.13.1) Been working in this same manner for a couple years with no issues until now.