Google reCaptcha says:invalid-request-cookie

this is my first time in using recaptcha on my website.

I'm using PHP API to validate the recaptcha, it keeps saying invalid-request-cookie

I found out on different forum that www.example.com is different with example.com, so I register my site again without www , but still it is not working..

When I verify the recaptcha_response_field and recaptcha_challenge_field the values are correct.

here is the captcha checker:

require_once(recaptchalib.php'); 

$publickey = "not displayed"; //for security
$privatekey = "not displayed"; //for security
$error = null; 

if( $_POST ) {
    $arr = array('a' => $_POST['task'], 'b' => $_POST['recaptcha_challenge_field'], 'c' => $_POST['recaptcha_response_field']);

    if( trim($arr['a']) == 'captcha' ) {
        $resp = null;
        $error = null;
        $captcha_result = 'success';
        $resp = recaptcha_check_answer( $privatekey, $_SERVER["REMOTE_ADDR"], $arr['b'], $arr['c'] );       

        if( $resp->error ){
            $captcha_result = 'fail';
        }
        echo $captcha_result;
    } 
}

here is the HTML code:

             <div id="captcha-div">
                <script type="text/javascript">
                          var RecaptchaOptions = {
                              tabindex: 1,
                              theme: 'custom',
                              custom_theme_widget: 'recaptcha_widget'
                          };
                        </script>
                <div id="recaptcha_widget" style="display:none"><div id="recaptcha_image" style="width: 200px; height: 57px; "></div>
                <?php echo recaptcha_get_html($publickey, $error); ?>
                <div class="recaptcha_only_if_incorrect_sol" style="color:red">Incorrect. Try Again.</div>
                <span class="recaptcha_only_if_audio">Type what you hear</span>
                <input type="text" id="recaptcha_response_field" name="recaptcha_response_field">
                <div class="recaptcha_only_if_audio"><a href="javascript:Recaptcha.switch_type(&#39;image&#39;)">Kumuha ng larawang CAPTCHA</a></div>

                <script type="text/javascript" src="http://www.google.com/recaptcha/api/challenge?k=6Le_X88SAAAAAAH3NEbkIr3w75SEQnQYwl96Y7f0"></script>
                <noscript><iframe src="http://www.google.com/recaptcha/api/noscript?k=6Le_X88SAAAAAAH3NEbkIr3w75SEQnQYwl96Y7f0" height="300" width="500" frameborder="0"></iframe><br>
                <textarea name="recaptcha_challenge_field" rows="3" cols="40">
                             </textarea>
                <input type="hidden" name="recaptcha_response_field" value="manual_challenge"></noscript></div>
                <script type="text/javascript">
                  window.onload = function() {
                      Recaptcha.focus_response_field();
                  }
                </script>
                <p id="captcha-error" style="color:red; font-weight:bold;"></p>
            </div>
            <div><a id="captcha-refresh" href="javascript:Recaptcha.reload()"></a></div>
            <div  class="recaptcha_only_if_image"><a id="captcha-audio" href="javascript:Recaptcha.switch_type(&#39;audio&#39;)"></a></div>
            <div><a id="captcha-help" href="javascript:Recaptcha.showhelp()"></a></div>
            <div id="circle-submit"></div>

can anyone help me out with this issue?

Thanks, Justin

As reCAPTCHA Support says:

No, this will not result in the invalid domain. What this means is that you are not submitting the recaptcha_challenge_field to the server correctly.

So make sure you rendering the form with recapcha corectly. Check out this link.