AS3 to PHP - mail() function

When I click on send the textbox displays 'sending....' with no change. I'm very sure that this was working before, but the client has noticed it not working recently. I can't find the problem, please help.

I have a swf with this AS3

var var_load:URLLoader = new URLLoader;  

var URL_request:URLRequest = new URLRequest( "http://www.blah.com/send_email_auto_response.php" );  

URL_request.method = URLRequestMethod.POST;  



function submit(e:MouseEvent):void

{  

    if( contact_name.text == "" || contact_email.text == "" ||

        contact_subject.text == "" || contact_message.text == "" )  

    {  

        message_status.text = "Please fill up all text fields.";  

    }  

    else if( !validate_email(contact_email.text) )  

    {  

        message_status.text = "Please enter the valid email address.";  

    }

    else  

    {  

        message_status.text = "sending...";     

        var email_data:String = "name=" + contact_name.text

                       + "&email=" + contact_email.text

                       + "&subject=" + contact_subject.text

                       + "&message=" + contact_message.text;



        var URL_vars:URLVariables = new URLVariables(email_data);

        URL_vars.dataFormat = URLLoaderDataFormat.TEXT;



        URL_request.data = URL_vars;

        var_load.load( URL_request );

        var_load.addEventListener(Event.COMPLETE, receive_response );

    }  

}

that calls a page with this PHP code..

$contact_name = $_POST['name'];    

$contact_email = $_POST['email'];    

$contact_subject = $_POST['subject'];  

$contact_message = $_POST['message'];  

if( $contact_name == true )  

{  

    $sender = $contact_email;  

    $receiver = "info@blah.com";  

    $client_ip = $_SERVER['REMOTE_ADDR'];  



    $email_body = "Name: $contact_name \nEmail: $sender \n\nSubject: $contact_subject \n\nMessage: \n\n$contact_message \n\nIP: $client_ip \n\n";  

    $email_body_auto_reply = "Hello $contact_name, \nThis is the auto reply message. Thank you.";  



    $extra = "From: $sender\r\n" . "Reply-To: $sender \r\n" . "X-Mailer: PHP/" . phpversion();

    $extra_auto_reply = "From: $receiver\r\n" . "Reply-To: $receiver \r\n" . "X-Mailer: PHP/" . phpversion();



    mail( $sender, "Auto Reply - Re: $contact_subject", $email_body_auto_reply, $extra_auto_reply );    // auto reply mail to sender



    if( mail( $receiver, "Flash Contact Form - $contact_subject", $email_body, $extra ) )

    {

        echo "success=yes";

    }

    else

    {

        echo "success=no";

    }

}