title: App Engine: The private key you've selected does not appear to be valid
body: <p>I'm trying to add a new SSL certificate to my Google App Engine account, but after following all the steps in <a href="https://cloud.google.com/appengine/docs/using-custom-domains-and-ssl#obtaining_a_certificate" rel="noreferrer">the manual</a> I kept getting this error uploading the Unencrypted PEM encoded RSA private key:</p>
  
  <blockquote>
    <p>The private key you've selected does not appear to be valid.</p>
  </blockquote>
  
  <p>Anyone have experienced this issue?</p>