I have the same problem and I guess this is a bug related to Ubuntu 13.04. My other apps which use the online accounts have stopped working too.
When launching the script manually, the following stacktrace is thrown:
Logging in as 'firstname.lastname@example.org'...
Error logging in as 'email@example.com'
'firstname.lastname@example.org' may not be a GNOME online account. A list of existing accounts is below.
If you do not see a list of accounts, then you first need to add one.
For more information, see http://library.gnome.org/users/gnome-help/stable/accounts.html
Traceback (most recent call last):
File "./gnome-shell-google-calendar.py", line 477, in <module>
account = oauth.oauth_prompt()
File "/home/tnaessens/gnome-shell-google-calendar/oauth.py", line 13, in oauth_prompt
File "/usr/lib/python2.7/dist-packages/dbus/bus.py", line 241, in get_object
File "/usr/lib/python2.7/dist-packages/dbus/proxies.py", line 248, in __init__
self._named_service = conn.activate_name_owner(bus_name)
File "/usr/lib/python2.7/dist-packages/dbus/bus.py", line 180, in activate_name_owner
File "/usr/lib/python2.7/dist-packages/dbus/bus.py", line 278, in start_service_by_name
'su', (bus_name, flags)))
File "/usr/lib/python2.7/dist-packages/dbus/connection.py", line 651, in call_blocking
dbus.exceptions.DBusException: org.freedesktop.DBus.Error.ServiceUnknown: The name org.gnome.OnlineAccounts was not provided by any .service files
When I went looking in the dbus-1/services directory, there was no org.gnome.OnlineAccounts.
Solution: I fixed this by downloading
gnome-online-accounts and by restarting the .py file. It asked for my account, I entered it and it immediatly started synchronizing.