Connect gmail via php imap? local issuer certificate error

I need to connect to my Gmail account using IMAPwith PHP. I have working code, but when I try to establish a connection, I get the following error:

Warning: imap_open () [function.imap-open]: Failed to open the stream {imap.gmail.com:993/ssl►►Gmail 022/All Mail in / home / demoosiz / public_html / goqlue / email. php on line 31
Cannot connect to Gmail: certificate failed for imap.gmail.com: local issuer certificate cannot be obtained: / C = US / O = Google Inc / CN = Google Internet Authority

my code is below

<?php
    /* connect to gmail */
    $hostname = '{imap.gmail.com:993/ssl}[Gmail]/All Mail';
    $username = 'hidden';
    $password = 'hidden';

    /* try to connect */
    $inbox = imap_open($hostname,$username,$password) or die('Cannot connect to Gmail: ' . imap_last_error());

    /* grab emails */
    $emails = imap_search($inbox,'ALL');

    /* if emails are returned, cycle through each... */
    if($emails) {

      /* begin output var */
      $output = '';

      /* put the newest emails on top */
      rsort($emails);

      /* for every email... */
      foreach($emails as $email_number) {

        /* get information specific to this email */
        $overview = imap_fetch_overview($inbox,$email_number,0);
        $message = imap_fetchbody($inbox,$email_number,2);

        /* output the email header information */
        $output.= '<div class="toggler '.($overview[0]->seen ? 'read' : 'unread').'">';
        $output.= '<span class="subject">'.$overview[0]->subject.'</span> ';
        $output.= '<span class="from">'.$overview[0]->from.'</span>';
        $output.= '<span class="date">on '.$overview[0]->date.'</span>';
        $output.= '</div>';

        /* output the email body */
        $output.= '<div class="body">'.$message.'</div>';
      }

      echo $output;
    } 

    /* close the connection */
    imap_close($inbox);
    ?>