django celery Getting TypeError: 'tuple' object is not callable

I've just installed celery on my local machine (win10) with RabbitMQ and followed their beginners tutorial . But I get the error message TypeError: 'tuple' object is not callable

src>workon clicknstrip
(clicknstrip) src>python manage.py celery beat

celery beat v3.1.18 (Cipater) is starting.
__    -    ... __   -        _
Configuration ->
    . broker -> amqp://guest:**@localhost:5672//
    . loader -> celery.loaders.app.AppLoader
    . scheduler -> celery.beat.PersistentScheduler
    . db -> celerybeat-schedule
    . logfile -> [stderr]@%INFO
    . maxinterval -> now (0s)
[2015-08-13 10:01:13,441: INFO/MainProcess] beat: Starting...
[2015-08-13 10:01:13,466: WARNING/MainProcess] DB Reset: Account for new __version__ field
[2015-08-13 10:01:13,470: CRITICAL/MainProcess] beat raised exception <type 'exceptions.TypeError'>: TypeError("'tuple' object is not callable",)
Traceback (most recent call last):
  File "clicknstrip\lib\site-packages\celery\apps\beat.py", line 112, in start_scheduler
    beat.start()
  File "clicknstrip\lib\site-packages\celery\beat.py", line 454, in start
    humanize_seconds(self.scheduler.max_interval))
  File "clicknstrip\lib\site-packages\kombu\utils\__init__.py", line 322, in __get__
    value = obj.__dict__[self.__name__] = self.__get(obj)
  File "clicknstrip\lib\site-packages\celery\beat.py", line 494, in scheduler
    return self.get_scheduler()
  File "clicknstrip\lib\site-packages\celery\beat.py", line 489, in get_scheduler
    lazy=lazy)
  File "clicknstrip\lib\site-packages\celery\utils\imports.py", line 53, in instantiate
    return symbol_by_name(name)(*args, **kwargs)
  File "clicknstrip\lib\site-packages\celery\beat.py", line 358, in __init__
    Scheduler.__init__(self, *args, **kwargs)
  File "clicknstrip\lib\site-packages\celery\beat.py", line 185, in __init__
    self.setup_schedule()
  File "clicknstrip\lib\site-packages\celery\beat.py", line 406, in setup_schedule
    self.install_default_entries(self.schedule)
  File "clicknstrip\lib\site-packages\celery\beat.py", line 190, in install_default_entries
    not self.app.backend.supports_autoexpire:
  File "clicknstrip\lib\site-packages\kombu\utils\__init__.py", line 322, in __get__
    value = obj.__dict__[self.__name__] = self.__get(obj)
  File "clicknstrip\lib\site-packages\celery\app\base.py", line 625, in backend
    return self._get_backend()
  File "clicknstrip\lib\site-packages\celery\app\base.py", line 444, in _get_backend
    return backend(app=self, url=url)
TypeError: 'tuple' object is not callable

This is my celery.py

from __future__ import absolute_import
import os
from celery import Celery

# set the default Django settings module for the 'celery' program.
os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'clicknstrip.settings.local')

from django.conf import settings

app = Celery('clicknstrip')

# Using a string here means the worker will not have to
# pickle the object when using Windows.
app.config_from_object('django.conf:settings')
app.autodiscover_tasks(lambda: settings.INSTALLED_APPS)


@app.task(bind=True)
def debug_task(self):
    print('Request: {0!r}'.format(self.request))

This is my task.py

from __future__ import absolute_import

from celery import shared_task


@shared_task
def add(x, y):
    return x + y


@shared_task
def mul(x, y):
    return x * y


@shared_task
def xsum(numbers):
    return sum(numbers)