speech_recognition: IOError: [Errno Input overflowed] -9981

I got this error after the recognition worked OK once.

Source code:

import speech_recognition as sr

r = sr.Recognizer()
m = sr.Microphone()
m.RATE = 44100
m.CHUNK = 512

print("A moment of silence, please...")
with m as source:
    r.adjust_for_ambient_noise(source)
    print("Set minimum energy threshold to {}".format(r.energy_threshold))
    while True:
        print("Say something!")
        audio = r.listen(source)
        print("Got it! Now to recognize it...")
        try:
            print("You said " + r.recognize(audio))
        except LookupError:
            print("Oops! Didn't catch that")

Error message:

A moment of silence, please...
ALSA lib pcm_dmix.c:957:(snd_pcm_dmix_open) The dmix plugin supports only playback stream
Cannot connect to server socket err = No such file or directory
Cannot connect to server request channel
jack server is not running or cannot be started
Set minimum energy threshold to 350.037988116
Say something!
Got it! Now to recognize it...
You said hello testing testing
Say something!
Traceback (most recent call last):
  File "listen.py", line 14, in <module>
    audio = r.listen(source)
  File "/usr/local/lib/python2.7/dist-packages/speech_recognition/__init__.py", line 265, in listen
    buffer = source.stream.read(source.CHUNK)
  File "/usr/lib/pymodules/python2.7/pyaudio.py", line 564, in read
    return pa.read_stream(self._stream, num_frames)
IOError: [Errno Input overflowed] -9981