locust error

stacktrace

[2015-04-17 10:39:36,405] odin/INFO/locust.runners: Client 'server.local_bcd20a7610ce99d654d2ef65cef7a28c' quit. Currently 0 clients connected.
[2015-04-17 10:43:40,631] odin/INFO/locust.runners: Client 'server.local_7f916f1d5997cf44f9f169ccf38e5c5e' reported as ready. Currently 1 clients ready to swarm.
[2015-04-17 10:43:47,857] odin/INFO/locust.runners: Sending hatch jobs to 1 ready clients
[2015-04-17 10:43:47,857] odin/ERROR/stderr: Traceback (most recent call last):
[2015-04-17 10:43:47,858] odin/ERROR/stderr: File "/usr/lib64/python2.7/site-packages/gevent/pywsgi.py", line 508, in handle_one_response
[2015-04-17 10:43:47,858] odin/ERROR/stderr: self.run_application()
[2015-04-17 10:43:47,858] odin/ERROR/stderr: File "/usr/lib64/python2.7/site-packages/gevent/pywsgi.py", line 494, in run_application
[2015-04-17 10:43:47,858] odin/ERROR/stderr: self.result = self.application(self.environ, self.start_response)
[2015-04-17 10:43:47,858] odin/ERROR/stderr: File "/usr/lib/python2.7/site-packages/flask/app.py", line 1836, in __call__
[2015-04-17 10:43:47,858] odin/ERROR/stderr: return self.wsgi_app(environ, start_response)
[2015-04-17 10:43:47,858] odin/ERROR/stderr: File "/usr/lib/python2.7/site-packages/flask/app.py", line 1820, in wsgi_app
[2015-04-17 10:43:47,858] odin/ERROR/stderr: response = self.make_response(self.handle_exception(e))
[2015-04-17 10:43:47,858] odin/ERROR/stderr: File "/usr/lib/python2.7/site-packages/flask/app.py", line 1403, in handle_exception
[2015-04-17 10:43:47,859] odin/ERROR/stderr: reraise(exc_type, exc_value, tb)
[2015-04-17 10:43:47,859] odin/ERROR/stderr: File "/usr/lib/python2.7/site-packages/flask/app.py", line 1817, in wsgi_app
[2015-04-17 10:43:47,859] odin/ERROR/stderr: response = self.full_dispatch_request()
[2015-04-17 10:43:47,859] odin/ERROR/stderr: File "/usr/lib/python2.7/site-packages/flask/app.py", line 1477, in full_dispatch_request
[2015-04-17 10:43:47,859] odin/ERROR/stderr: rv = self.handle_user_exception(e)
[2015-04-17 10:43:47,859] odin/ERROR/stderr: File "/usr/lib/python2.7/site-packages/flask/app.py", line 1381, in handle_user_exception
[2015-04-17 10:43:47,859] odin/ERROR/stderr: reraise(exc_type, exc_value, tb)
[2015-04-17 10:43:47,859] odin/ERROR/stderr: File "/usr/lib/python2.7/site-packages/flask/app.py", line 1475, in full_dispatch_request
[2015-04-17 10:43:47,859] odin/ERROR/stderr: rv = self.dispatch_request()
[2015-04-17 10:43:47,860] odin/ERROR/stderr: File "/usr/lib/python2.7/site-packages/flask/app.py", line 1461, in dispatch_request
[2015-04-17 10:43:47,860] odin/ERROR/stderr: return self.view_functions[rule.endpoint](**req.view_args)
[2015-04-17 10:43:47,860] odin/ERROR/stderr: File "/usr/lib/python2.7/site-packages/locust/web.py", line 51, in swarm
[2015-04-17 10:43:47,860] odin/ERROR/stderr: runners.locust_runner.start_hatching(locust_count, hatch_rate)
[2015-04-17 10:43:47,860] odin/ERROR/stderr: File "/usr/lib/python2.7/site-packages/locust/runners.py", line 297, in start_hatching
[2015-04-17 10:43:47,860] odin/ERROR/stderr: self.server.send(Message("hatch", data, None))
[2015-04-17 10:43:47,860] odin/ERROR/stderr: File "/usr/lib/python2.7/site-packages/locust/rpc/zmqrpc.py", line 7, in send
[2015-04-17 10:43:47,860] odin/ERROR/stderr: self.sender.send(msg.serialize())
[2015-04-17 10:43:47,860] odin/ERROR/stderr: File "/usr/lib64/python2.7/site-packages/zmq/green/core.py", line 215, in send
[2015-04-17 10:43:47,861] odin/ERROR/stderr: self._wait_write()
[2015-04-17 10:43:47,861] odin/ERROR/stderr: File "/usr/lib64/python2.7/site-packages/zmq/green/core.py", line 124, in _wait_write
[2015-04-17 10:43:47,861] odin/ERROR/stderr: assert self.__writable.ready(), "Only one greenlet can be waiting on this event"
[2015-04-17 10:43:47,861] odin/ERROR/stderr: AssertionError: Only one greenlet can be waiting on this event
[2015-04-17 10:43:47,864] odin/ERROR/stderr: {'CONTENT_LENGTH': '30',

Ever find out what this error was caused by? I'm getting the same thing on Ubuntu 14.04.