I have been trying to utilize json in this jQuery.post because I need to return two values from my executed php.  The code was working when I was not implementing json.  I need to see if a promo code entered is valid for a particular broker.  The two variables I need back are the instant message whether or not it's valid (this is displayed to the user) and I need to update a hidden field that will be used later while updating the database.
The jQuery.post does not seem to be firing at all, but the code directly above it (the ajax-loader.gif) is working.
I did re-write the whole thing at one point using jQuery.ajax, and had issues there too.  Granted, I have probably been looking at this too long and have tried to re-write too many times, but any help is greatly appreciated!!
Here's the jQuery.post
<!-- Below Script is for Checking Promo Code Against Database-->
<script type="text/javascript">
jQuery(document).ready(function() {
jQuery("#promocode").keyup(function (e) {
    //removes spaces from PromoCode
    jQuery(this).val(jQuery(this).val().replace(/\s/g, ''));
    var promocode = jQuery(this).val();
    var brokerdealerid = document.getElementById("BrokerDealerId").value;
    if(promocode.length > 0 ){
        jQuery("#promo-result").html('<img src="../imgs/ajax-loader.gif" />');
        jQuery.post(
                '../check_promocode.php', 
                {promocode:promocode, brokerdealerid:brokerdealerid}, 
                function(data) {
                $("#promo-result").html(data.promoresult);
                $("#promo-result-valid").html(data.promovalid);
                },
                "json");
    }
}); 
});
</script>
<!-- End Script is for Checking Promo Code Against Database-->
Here's relevant code from check_promocode.php:
    //sanitize incoming parameters
if (isset($_POST['brokerdealerid'])) $brokerdealerid = sanitizeMySQL($_POST['brokerdealerid']);
$promocode = sanitizeMySQL($promocode);
//check promocode in db
$results = mysql_query("SELECT PromotionCodeIdentifier FROM PromotionCode WHERE PromotionCodeIdentifier='$promocode' AND BrokerDealerId='$brokerdealerid' AND PromotionCodStrtDte <= CURDATE() AND PromotionCodExpDte >= CURDATE()");
//return total count
$PromoCode_exist = mysql_num_rows($results); //total records
//if value is more than 0, promocode is valid
    if($PromoCode_exist) 
    {
        echo json_encode(array("promoresult"=>"Promotion Code Valid", "promovalid"=>"Y"));
        exit();
    }else{
        echo json_encode(array("promoresult"=>"Invalid Promotion Code", "promovalid"=>"N"));
        exit();
    }