跟著官方的入門教程部署和運行的，為啥報這個錯？

tasks.py

# -*- encoding:UTF-8 -*-

from celery import Celery

brokers = 'redis://localhost:6379'
backend = 'redis://localhost:6379'

app = Celery('tasks', broker=brokers, backend=backend)
app.control.purge()


@app.task
def add(x, y):
    return x + y

>>> from tasks import add
>>> add.delay(6,6)
<AsyncResult: e1b8521e-e8a1-4431-8232-b0cbe7a35e9e>

[2017-08-08 19:14:32,580: ERROR/MainProcess] Task handler raised error: ValueErr
or('not enough values to unpack (expected 3, got 0)',)
Traceback (most recent call last):
  File "c:\python352\lib\site-packages\billiard\pool.py", line 358, in workloop
    result = (True, prepare_result(fun(*args, **kwargs)))
  File "c:\python352\lib\site-packages\celery\app\trace.py", line 525, in _fast_
trace_task
    tasks, accept, hostname = _loc
ValueError: not enough values to unpack (expected 3, got 0)
[2017-08-08 19:15:46,049: ERROR/MainProcess] Task handler raised error: ValueErr
or('not enough values to unpack (expected 3, got 0)',)
Traceback (most recent call last):
  File "c:\python352\lib\site-packages\billiard\pool.py", line 358, in workloop
    result = (True, prepare_result(fun(*args, **kwargs)))
  File "c:\python352\lib\site-packages\celery\app\trace.py", line 525, in _fast_
trace_task
    tasks, accept, hostname = _loc
ValueError: not enough values to unpack (expected 3, got 0)