title: The session id is too long or contains illegal characters
body: <p>I've got a problem on a site where sometimes there is logged an warning like:</p>
  
  <pre><code>session_start() [&lt;a href='0function.session-start0'&gt;function.session-start0&lt;/a&gt;]: The session id is too long or contains illegal characters, valid characters are a-z, A-Z, 0-9 and '-,'
  </code></pre>
  
  <p>I went further and dumped the <code>$_SERVER</code> variable:</p>
  
  <p><code>[HTTP_COOKIE] =&gt; name2=; name1=; my_session=; __gads=; __utma=; __utmc=; __utmz=</code></p>
  
  <p>The requests are coming all over the world, they are not many, 1-2 per day which comes in this format ( I mean all cookies seam to be empty? ).</p>
  
  <p>Any clue in what conditions and why is this happening ? An how this should be handled ? <code>session_regenerate_id()</code> does nothing I still get the same warning </p>