[dbus] get_tasks method not working

Call the get_tasks method with dbus, you will have the following error :

org.GTG
Traceback (most recent call last):
  File "newtask.py", line 27, in <module>
    get_task()
  File "newtask.py", line 23, in get_task
    print timi.get_tasks()
  File "/usr/lib/pymodules/python2.6/dbus/proxies.py", line 68, in __call__
    return self._proxy_method(*args, **keywords)
  File "/usr/lib/pymodules/python2.6/dbus/proxies.py", line 140, in __call__
    **keywords)
  File "/usr/lib/pymodules/python2.6/dbus/connection.py", line 620, in call_blocking
    message, timeout)
dbus.exceptions.DBusException: org.freedesktop.DBus.Python.TypeError: Traceback (most recent call last):
  File "/usr/lib/pymodules/python2.6/dbus/service.py", line 745, in _message_cb
    _method_reply_return(connection, message, method_name, signature, *retval)
  File "/usr/lib/pymodules/python2.6/dbus/service.py", line 252, in _method_reply_return
    reply.append(signature=signature, *retval)
TypeError: Don't know how which D-Bus type to use to encode type "instance"