Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/defer/__init__.py", line 472, in _inline_callbacks
    result = gen.throw(result.type, result.value, result.traceback)
  File "/usr/share/software-center/softwarecenter/backend/aptd.py", line 638, in _medium_required
    yield transaction.cancel(defer=True)
AptDaemonError: org.debian.apt: Could not cancel transaction