title: Python Selenium finds the input element but cannot send_keys
body: <p>I am trying to write a string into an <code>&lt;input&gt;</code> element using Selenium web driver and Python in Windows.</p>
  
  <p>The element it's located and selected, but the webdriver fails when trying to <code>send_keys("mystring")</code>.</p>
  
  <pre><code>campotx = driver.find_element_by_css_selector("input.urEdf2TxtRadius.urEdf2TxtEnbl.urEdfVAlign")
  campotx.click()
  campotx.clear() 
  ##########----it works ok until here
  campotx.send_keys("SM37")
  campotx.send_keys(Keys.ENTER)
  </code></pre>
  
  <p>The issue is not related to the "find element" method: I tried by_ID, by_class_name and by_xpath. All of them are able to locate the element. I am only not able to <code>send_keys</code>.</p>
  
  <p>I am using HTMLUNITS, the headless webdriver. The output error for this issue is rare, I tried googleing it but can't find anything:</p>
  
  <pre><code>selenium.common.exceptions.WebDriverException: Message: TypeError: Cannot call method "setOpenerRef" of null (http://myurl.com)
  </code></pre>
  
  <p>Here is the <code>&lt;input&gt;</code> source code:</p>
  
  <pre><code>&lt;input id="ToolbarOkCode" ct="I" lsdata="{0:'ToolbarOkCode',1:'Command',4:200,13:'150px',23:true}" lsevents="{Change:[{ClientAction:'none'},{type:'TOOLBARINPUTFIELD'}],Enter:[{ClientAction:'submit',PrepareScript:'return\x20its.XControlSubmit\x28\x29\x3b',ResponseData:'delta',TransportMethod:'partial'},{Submit:'X',type:'TOOLBARINPUTFIELD'}]}" type="text" maxlength="200" tabindex="0" ti="0" title="Command" class="urEdf2TxtRadius urEdf2TxtEnbl urEdfVAlign" value="" autocomplete="on" autocorrect="off" name="ToolbarOkCode" style="width:150px;"/&gt;
  </code></pre>
  
  <p><strong>EDIT:</strong> </p>
  
  <ul>
  <li>Tried to use PhantomJS but I was not able to logon.</li>
  <li>Tried to use headless_ie_selenium.exe but I couldn't even start the driver.</li>
  <li>Tried to use the headless chrome, same issue than headless_ie_selenium.All the tutorials are related to Linux environments.</li>
  </ul>