PHP Ajax jQuery Post - What have I done wrong?

This is my jQuery...

$.ajax({
                type: 'POST',
                url: 'http://adamscarter.co.uk/daily/facebook/savefbprofile.php',
                data: {'fb_id': fb_id, 'fbusername': fbusername, 'location_id': location_id, 'gender': gender},
                beforeSend: function() {
                    console.log('Before send: ' + fb_id, fbusername, location_id, gender);
                },
                success: function(data) {
                    console.log('saveFbProfile post ajax success');
                    console.log(data);
                }
            });

...and this is my PHP...

<?php
session_start();

include('dbcon.php');

$gender = substr($_POST['gender'], 0, 1);
$fb_id = $_POST['fb_id'];
$location_id = $_POST['location_id'];
$fbusername = $_POST['fbusername'];

//Set session vars
$_SESSION['gender'] = $gender;
$_SESSION['fb_id'] = $fb_id;
$_SESSION['location_id'] = $location_id;
$_SESSION['fbusername'] = $fbusername;

if (isset($_SESSION['userid'])) {
    mysql_select_db('users', $GLOBALS['conInsert']);
    $sql = "UPDATE user_fb_details SET gender = '". $gender. "', fb_id = '". $fb_id. "', location_id = '". $location_id. "', username = '". $fbusername. "' WHERE user_id = '". $_SESSION['userid']. "'";
    mysql_qu开发者_StackOverflow中文版ery($sql, $GLOBALS['conInsert']);
}
?>

Is there a mistake in my code? When I log the variables they all have the correct value, but i just get a 'parseerror'.

Sounds like jQuery might be trying to parse the result of the POST as a JSON response and failing as it's not JSON. You might want to set the dataType to 'text', or return a different Content-Type from the PHP.

And you'll definitely want to fix your dangerous SQL-injection holes with a bit of mysql_real_escape_string or parameterised queries.