Ubuntu One returns IPCError during startup

[rpgmr]

See log file controlpanel.log for errors:

2013-09-27 15:59:43,682 - ubuntuone.controlpanel.backend - INFO - ControlBackend: instance started.
2013-09-27 15:59:44,247 - ubuntuone.controlpanel.qt.gui - INFO - Updates available? None
2013-09-27 15:59:46,361 - ubuntuone.controlpanel.qt.folders - ERROR - Error while invoking <bound method FoldersPanel.load of <ubuntuone.controlpanel.gui.qt.folders.FoldersPanel object at 0x9e4180c>> with args () and kwargs {}:
Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/ubuntuone-control-panel/ubuntuone/controlpanel/gui/qt/__init__.py", line 100, in inner
    res = yield f(*args, **kwargs)
IPCError: org.freedesktop.DBus.Error.UnknownMethod:
2013-09-27 15:59:51,556 - ubuntuone.controlpanel.qt.folders - INFO - The warning dialog was shown and also closed (message was 'IPCError').

Steps:

0) Ubuntu One was working for once, downloaded files successfully, then on next reboot, complaint "IPCEror".
1) Commpletely remove ubuntuone-client
2) find . -name *ubuntuone* -exec rm -rf {} \;
3) Invoke Ubuntu One, let it install the client
4) Run Ubuntu One, and it'll still show you the "IPCError"

Version 3.0.1-0ubuntu1 of the following packages:

ubuntuone-control-panel-qt /
ubuntuone-control-panel-common /
ubuntuone-control-panel /
python-ubuntuone-control-panel

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.