title: "Message: unknown error: cannot focus element" in python selenium driver
body: <p>Why does this piece of code throw an exception <code>selenium.common.exceptions.WebDriverException: Message: unknown error: cannot focus element</code>? </p>
  
  <p>As far as I can tell, I'm choosing the right element. Googling suggested to have a <code>.click()</code> on element before sending keys but that didn't help either.</p>
  
  <pre><code>from selenium import webdriver
  from selenium.common.exceptions import TimeoutException
  from selenium.webdriver.common.by import By
  from selenium.webdriver.support.ui import WebDriverWait
  from selenium.webdriver.support import expected_conditions as EC
  from selenium.webdriver.common.keys import Keys
  
  driver = webdriver.Chrome()
  driver.get("https://netbanking.hdfcbank.com/netbanking/")
  login_wait = WebDriverWait(driver, 10)
  
  assert "Welcome to HDFC Bank" in driver.title
  
  frame = login_wait.until(EC.presence_of_element_located((By.NAME, 'login_page')))
  driver.switch_to.frame(frame)
  
  try:
      elem = login_wait.until(EC.presence_of_element_located((By.CLASS_NAME, 'pwd_field')))
      print("Page is ready!")
      elem.send_keys("123456")
      elem.send_keys(Keys.RETURN)
  except TimeoutException:
      print("Loading took too much time!")
  
  driver.close()
  </code></pre>