Unable to restart HA

Installation
1

i did check the config file but then i see:

(homeassistant) homeassistant@raspberrypi:/home/pi $ hass
Traceback (most recent call last):
  File "/srv/homeassistant/bin/hass", line 7, in <module>
    from homeassistant.__main__ import main
  File "/srv/homeassistant/lib/python3.4/site-packages/homeassistant/__main__.py", line 20, in <module>
    from homeassistant.util.async import run_callback_threadsafe
ImportError: No module named 'homeassistant.util.async'
(homeassistant) homeassistant@raspberrypi:/home/pi $

someone and sollution?