尝试运行代码时出现此错误：

oauth2client.client.AccessTokenRefreshError: unauthorized_client: Unauthorized client or scope in request.

这是我的代码：

import json
import requests
import httplib2
from oauth2client.client import SignedJwtAssertionCredentials
from apiclient.discovery import build

if __name__ == '__main__':

    json_key_file = 'my-key.json'

    with open(json_key_file) as json_file:

        json_data = json.load(json_file)
        credential = SignedJwtAssertionCredentials(json_data['client_email'], json_data['client_email'], json_data['private_key'], scope=['https://www.googleapis.com/auth/admin.directory.user','https://www.googleapis.com/auth/admin.directory.user.readonly'], sub='myemail@domain.com')

    http = httplib2.Http()
    http = credential.authorize(http)

    service = build('admin', 'directory_v1', http=http)
    data = service.users().list(domain='domain.com').execute()

    print data

我在控制台中正确设置了作用域，并且在控制台中启用了我的Admin SDK。我的电子邮件是超级管理员，可以访问所有Admin API特权。

为什么会出现此错误？