The bug ist still not fixed for me...

2012-06-02 17:35:40,477 - softwarecenter.ui.gtk3.app - INFO - setting up proxy 'None'
2012-06-02 17:35:40,481 - softwarecenter.db.database - INFO - open() database: path=None use_axi=True use_agent=True
2012-06-02 17:35:40,615 - softwarecenter.backend.reviews - WARNING - Could not get usefulness from server, no username in config file
2012-06-02 17:35:40,734 - softwarecenter.db.pkginfo_impl.aptcache - INFO - aptcache.open()
2012-06-02 17:35:40,765 - softwarecenter.backend.spawn_helper - WARNING - exit code 1 from helper for '['/usr/share/software-center/piston_generic_helper.py', '--datadir', '/usr/share/software-center/', 'RatingsAndReviewsAPI', 'review_stats']'
2012-06-02 17:35:40,765 - softwarecenter.backend.spawn_helper - WARNING - got error from helper: 'ERROR:__main__:urclient_apps
Traceback (most recent call last):
  File "/usr/share/software-center/piston_generic_helper.py", line 214, in <module>
    piston_reply = f(**kwargs)
  File "/usr/lib/python2.7/dist-packages/piston_mini_client/validators.py", line 44, in wrapper
    return func(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/piston_mini_client/validators.py", line 44, in wrapper
    return func(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/piston_mini_client/validators.py", line 65, in wrapper
    return func(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/piston_mini_client/__init__.py", line 136, in wrapper
    body = func(self, *args, **kwargs)
  File "/usr/share/software-center/softwarecenter/backend/piston/rnrclient_pristine.py", line 97, in review_stats
    return self._get(url, scheme=PUBLIC_API_SCHEME)
  File "/usr/lib/python2.7/dist-packages/piston_mini_client/__init__.py", line 356, in _get
    headers=headers)
  File "/usr/lib/python2.7/dist-packages/piston_mini_client/__init__.py", line 511, in _request
    method=method, body=body, headers=headers)
  File "/usr/local/lib/python2.7/dist-packages/httplib2/__init__.py", line 972, in request
    cached_value = self.cache.get(cachekey)
  File "/usr/local/lib/python2.7/dist-packages/httplib2/__init__.py", line 619, in get
    cacheFullPath = os.path.join(self.cache, self.safe(key))
  File "/usr/lib/python2.7/dist-packages/piston_mini_client/__init__.py", line 70, in safename
    filemd5 = _md5(filename).hexdigest()
AttributeError: 'NoneType' object has no attribute 'hexdigest'
'
2012-06-02 17:35:43,011 - softwarecenter.backend.spawn_helper - WARNING - exit code 1 from helper for '['/usr/share/software-center/piston_generic_helper.py', '--datadir', '/usr/share/software-center/', 'SoftwareCenterAgentAPI', 'exhibits', '{"lang": "de", "series": "precise"}']'
2012-06-02 17:35:43,012 - softwarecenter.backend.spawn_helper - WARNING - got error from helper: 'ERROR:__main__:urclient_apps
Traceback (most recent call last):
  File "/usr/share/software-center/piston_generic_helper.py", line 214, in <module>
    piston_reply = f(**kwargs)
  File "/usr/lib/python2.7/dist-packages/piston_mini_client/validators.py", line 44, in wrapper
    return func(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/piston_mini_client/validators.py", line 44, in wrapper
    return func(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/piston_mini_client/__init__.py", line 136, in wrapper
    body = func(self, *args, **kwargs)
  File "/usr/share/software-center/softwarecenter/backend/piston/scaclient_pristine.py", line 59, in exhibits
    return self._get(url)
  File "/usr/lib/python2.7/dist-packages/piston_mini_client/__init__.py", line 356, in _get
    headers=headers)
  File "/usr/lib/python2.7/dist-packages/piston_mini_client/__init__.py", line 511, in _request
    method=method, body=body, headers=headers)
  File "/usr/local/lib/python2.7/dist-packages/httplib2/__init__.py", line 972, in request
    cached_value = self.cache.get(cachekey)
  File "/usr/local/lib/python2.7/dist-packages/httplib2/__init__.py", line 619, in get
    cacheFullPath = os.path.join(self.cache, self.safe(key))
  File "/usr/lib/python2.7/dist-packages/piston_mini_client/__init__.py", line 70, in safename
    filemd5 = _md5(filename).hexdigest()
AttributeError: 'NoneType' object has no attribute 'hexdigest'
'
2012-06-02 17:35:45,027 - softwarecenter.backend.spawn_helper - WARNING - exit code 1 from helper for '['/usr/share/software-center/piston_generic_helper.py', '--datadir', '/usr/share/software-center/', 'SoftwareCenterAgentAPI', 'available_apps', '{"lang": "de", "series": "precise", "arch": "amd64"}']'
2012-06-02 17:35:45,028 - softwarecenter.backend.spawn_helper - WARNING - got error from helper: 'ERROR:__main__:urclient_apps
Traceback (most recent call last):
  File "/usr/share/software-center/piston_generic_helper.py", line 214, in <module>
    piston_reply = f(**kwargs)
  File "/usr/lib/python2.7/dist-packages/piston_mini_client/validators.py", line 44, in wrapper
    return func(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/piston_mini_client/validators.py", line 44, in wrapper
    return func(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/piston_mini_client/validators.py", line 44, in wrapper
    return func(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/piston_mini_client/__init__.py", line 136, in wrapper
    body = func(self, *args, **kwargs)
  File "/usr/share/software-center/softwarecenter/backend/piston/scaclient_pristine.py", line 23, in available_apps
    scheme=PUBLIC_API_SCHEME)
  File "/usr/lib/python2.7/dist-packages/piston_mini_client/__init__.py", line 356, in _get
    headers=headers)
  File "/usr/lib/python2.7/dist-packages/piston_mini_client/__init__.py", line 511, in _request
    method=method, body=body, headers=headers)
  File "/usr/local/lib/python2.7/dist-packages/httplib2/__init__.py", line 972, in request
    cached_value = self.cache.get(cachekey)
  File "/usr/local/lib/python2.7/dist-packages/httplib2/__init__.py", line 619, in get
    cacheFullPath = os.path.join(self.cache, self.safe(key))
  File "/usr/lib/python2.7/dist-packages/piston_mini_client/__init__.py", line 70, in safename
    filemd5 = _md5(filename).hexdigest()
AttributeError: 'NoneType' object has no attribute 'hexdigest'
'
2012-06-02 17:35:45,028 - softwarecenter.db.update - WARNING - error: ERROR:__main__:urclient_apps
Traceback (most recent call last):
  File "/usr/share/software-center/piston_generic_helper.py", line 214, in <module>
    piston_reply = f(**kwargs)
  File "/usr/lib/python2.7/dist-packages/piston_mini_client/validators.py", line 44, in wrapper
    return func(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/piston_mini_client/validators.py", line 44, in wrapper
    return func(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/piston_mini_client/validators.py", line 44, in wrapper
    return func(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/piston_mini_client/__init__.py", line 136, in wrapper
    body = func(self, *args, **kwargs)
  File "/usr/share/software-center/softwarecenter/backend/piston/scaclient_pristine.py", line 23, in available_apps
    scheme=PUBLIC_API_SCHEME)
  File "/usr/lib/python2.7/dist-packages/piston_mini_client/__init__.py", line 356, in _get
    headers=headers)
  File "/usr/lib/python2.7/dist-packages/piston_mini_client/__init__.py", line 511, in _request
    method=method, body=body, headers=headers)
  File "/usr/local/lib/python2.7/dist-packages/httplib2/__init__.py", line 972, in request
    cached_value = self.cache.get(cachekey)
  File "/usr/local/lib/python2.7/dist-packages/httplib2/__init__.py", line 619, in get
    cacheFullPath = os.path.join(self.cache, self.safe(key))
  File "/usr/lib/python2.7/dist-packages/piston_mini_client/__init__.py", line 70, in safename
    filemd5 = _md5(filename).hexdigest()
AttributeError: 'NoneType' object has no attribute 'hexdigest'

2012-06-02 17:35:45,071 - softwarecenter.ui.gtk3.app - INFO - software-center-agent finished with status 1