Eu continuo recebendo o seguinte erro quando executo meu código:

An error occurred: <HttpError 403 when requesting https://www.googleapis.com/gmail/v1/users/me/messages/send?alt=json returned "Insufficient Permission">

Este é o meu código:

import httplib2
import os
from httplib2 import Http

from apiclient import discovery
import oauth2client
from oauth2client import client
from oauth2client import tools

try:
    import argparse
    flags = argparse.ArgumentParser(parents=[tools.argparser]).parse_args()
except ImportError:
    flags = None

#SCOPES = 'https://www.googleapis.com/'
SCOPES = 'https://www.googleapis.com/auth/gmail.compose'
CLIENT_SECRET_FILE = 'client_secret.json'
APPLICATION_NAME = 'Gmail API Quickstart'

def get_credentials():
    """Gets valid user credentials from storage.

    If nothing has been stored, or if the stored credentials are invalid,
    the OAuth2 flow is completed to obtain the new credentials.

    Returns:
        Credentials, the obtained credential.
    """
    home_dir = os.path.expanduser('~')
    credential_dir = os.path.join(home_dir, '.credentials')
    if not os.path.exists(credential_dir):
        os.makedirs(credential_dir)
    credential_path = os.path.join(credential_dir,
                                   'gmail-quickstart.json')

    store = oauth2client.file.Storage(credential_path)
    credentials = store.get()
    if not credentials or credentials.invalid:
        flow = client.flow_from_clientsecrets(CLIENT_SECRET_FILE, SCOPES)
        flow.user_agent = APPLICATION_NAME
        if flags:
            credentials = tools.run_flow(flow, store, flags)
        else: # Needed only for compatability with Python 2.6
            credentials = tools.run(flow, store)
        print 'Storing credentials to ' + credential_path
    return credentials

def CreateMessage(sender, to, subject, message_text):
  """Create a message for an email.

  Args:
    sender: Email address of the sender.
    to: Email address of the receiver.
    subject: The subject of the email message.
    message_text: The text of the email message.

  Returns:
    An object containing a base64 encoded email object.
  """
  message = MIMEText(message_text)
  message['to'] = to
  message['from'] = sender
  message['subject'] = subject
  return {'raw': base64.b64encode(message.as_string())}

testMessage = CreateMessage('ENTER SENDERS EMAIL ADDRESS', 'ENTER RECEIVERRS EMAIL ADDRESS', 'ENTER SUBJECT', 'ENTER EMAIL BODY')

def SendMessage(service, user_id, message):
  """Send an email message.

  Args:
    service: Authorized Gmail API service instance.
    user_id: User's email address. The special value "me"
    can be used to indicate the authenticated user.
    message: Message to be sent.

  Returns:
    Sent Message.
  """
  try:
    message = (service.users().messages().send(userId=user_id, body=message)
               .execute())
    print 'Message Id: %s' % message['id']
    return message
  except errors.HttpError, error:
    print 'An error occurred: %s' % error


testSend = SendMessage(service, 'me', testMessage)

Continuo lendo que preciso editar um arquivo de credenciais, mas não consigo encontrá-lo. Eu tenho o Windows 7 instalado. Alguém sabe o que eu preciso fazer para superar esse erro? Eu sou um noob total nisso, então por favor, desculpe-me se eu parecer um pouco nooby sobre isso. Obrigado!