Ember CLI throws Unhandled 'error' event message

Ember CLI works great most of the time on my laptop. However, once in a while (very very occasionally) when I ctrl + c the ember server process and restart it, it throws the following error and refuses to start again until I do a complete system restart (I am on a Mac):

MacBook-Pro:client-web User$ ember server
version: 1.13.6
Could not find watchman, falling back to NodeWatcher for file system events.
Visit http://ift.tt/1PK1A1H for more info.
2015-09-04 17:46 ember[1102] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
2015-09-04 17:46 ember[1102] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
Livereload server on http://localhost:49152
Serving on http://localhost:4200/
2015-09-04 17:46 ember[1102] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)
events.js:85
      throw er; // Unhandled 'error' event
            ^
Error: watch EMFILE
    at exports._errnoException (util.js:746:11)
    at FSEvent.FSWatcher._handle.onchange (fs.js:1157:26)

Why does this happen? I want to avoid doing system restarts.