Programs that sync files such as dropbox, git etc use inotify to notice changes to the file system. The limit can be see by

cat /proc/sys/fs/inotify/max_user_watches
If you are running Debian, RedHat, or another similar Linux distribution, run the following in a terminal:
echo fs.inotify.max_user_watches=524288 | sudo tee -a /etc/sysctl.conf && sudo sysctl -p

If you are running ArchLinux, run the following command instead (see here for why):
echo fs.inotify.max_user_watches=524288 | sudo tee /etc/sysctl.d/40-max-user-watches.conf && sudo sysctl --system

close terminal and open against