我正在尝试使用Python中的Selenium用我的GMail帐户自动登录，但出现此错误：

selenium.common.exceptions.ElementNotVisibleException: Message: Element is not currently visible and so may not be interacted with

我的代码如下所示：

#!/usr/bin/python
# coding: utf8

import scrapy

from selenium import webdriver
from scrapy.selector import Selector
from selenium.webdriver.common.action_chains import ActionChains
from scrapy.contrib.spiders import CrawlSpider
from scrapy.selector import HtmlXPathSelector
from scrapy.contrib.linkextractors.sgml import SgmlLinkExtractor
from scrapy.contrib.spiders import CrawlSpider, Rule
from scrapy.http import Request, FormRequest
from scrapy import log
from scrapy.exceptions import DropItem
from scrapy import signals
from selenium.webdriver.common.by import By
import scrapy
from scrapy import signals
from scrapy.http import TextResponse 
from scrapy.xlib.pydispatch import dispatcher
from selenium import webdriver
from selenium.webdriver.common.keys import Keys


class googleplay(CrawlSpider):
    name = "selenium"
    flag = True

    def __init__(self):
        self.driver = webdriver.Firefox()
        self.driver.get('http://gmail.com')
        action = webdriver.ActionChains(self.driver)
        #User name input field identification and data entered
        usernametext = self.driver.find_element_by_name('Email')
        usernametext.send_keys("myemailaddress@gmail.com") #put your actual username
        self.driver.find_element_by_name('signIn').click()
        time.sleep(2)
        #Password input field identification and data entered
        passwordtext = self.driver.find_element_by_name('Passwd')
        passwordtext.send_keys("password") #put your actual password
        key = self.driver.find_element_by_name('signIn')
        print "----------------------"
        key.click()
        print "----------------------"
        start_urls = ["https://www.mywebsite.com"]

    def parse(self, reponse):
        #Loading the gmail URL
        print "toto"

我该如何解决我的问题？