File monitoring failed for project at "~/Dropbox/Rprojects/AdelieTranquil"
Error 28 (inotify_add_watch: No watches available)
In my case, I got this warning to go away by halting the Dropbox daemon. Apparently it soaks up a huge number of inotifys. Dropbox recommended running (on Linux)
echo fs.inotify.max_user_watches=100000 | sudo tee -a /etc/sysctl.conf; sudo sysctl -p