How to correctly send serialized data to php

See more:

PHP

Ajax

jQuery

So I am working on a php/jquery powered chat. Most of the features work, but when I try to submit a message, the jQuery doesn't seem to properly connect with the PHP and nothing happens. The PHP script works fine on it's own when I removed jQuery from the picture, so I'm certain it's the jQuery that's messing things up.

I hardcoded a value into data: and the messages would appear fine (with every message being that value, as expected). It's when I replace it with

$("#cbox_input").serialize(),

that things stopped posting.

Here is the code used in the chat.

<div id="cbox" align="left">
<script>
$(document).ready(function() {
    setInterval(function(){getUpdates()}, 2000);

function getUpdates() {
    $("#cbox").load("/lib/chat_post.php");
}

$("#submitmsg").click(function (event) {
    event.preventDefault();
        $.ajax({
          type: 'POST',
          url: '/lib/chat_new.php',
          data: $("#cbox_input").serialize(),
          success: function(){getUpdates()}
            });
        });
});
</script>
</div>

<form name="cbox_input" method='post' id="cbox_input">
    <input name="usermsg" id='usermsg' type="text" size="63" maxlength="255" />
    <input name="submitmsg" id='submitmsg' type="submit" />
</form>

And here is chat_new.php in case it is something there that is throwing a wrench in things.

	ob_start();
	session_start();
	require "/home3/himowa/public_html/life/inc/functions.php";
	
	$username = $_SESSION['login'];
	$ug = $_SESSION['user_group'];

	if ($_POST['submitmsg']){
		if ($username) {
			$text = $_POST['usermsg'];
			$text = stripslashes($text);
			$text = mysqli_real_escape_string($db,$text);
			
			if ($text) {
$sql = <<<SQL
    INSERT INTO chat_entries(author,text)
    values('$username','$text')
SQL;
			$result = $db->query($sql);
		}
	}
	
	if (!$username) {
		$ip = $_SERVER['REMOTE_ADDR'];
		
$sqlm = <<<SQL
    SELECT *
    FROM `chat_guests`
	WHERE ip = '$ip'
SQL;

		$resultm = $db->query($sqlm);
		$countm = $resultm->num_rows;
		if($countm == 0) {
$sqlg = <<<SQL
    INSERT INTO chat_guests(ip)
    values('$ip')
SQL;

		$resultg = $db->query($sqlg);
		}
		
		$resultm = $db->query($sqlm);
		$countm = $resultm->num_rows;
		if($countm == 1) {
			while ($rowm = mysqli_fetch_array($resultm)) {
				$gid = $rowm['id'];
			}
			$username = "Guest" . $gid;
			$text = $_POST['usermsg'];
			$text = stripslashes($text);
			$text = mysqli_real_escape_string($db,$text);
			
			if ($text) {
$sql = <<<SQL
    INSERT INTO chat_entries(author,text)
    values('$username','$text')
SQL;
			$result = $db->query($sql);
		}
	}
}
}