PHP异常对象错误

Question

Well the subject says most of it. I have a javascript function that uses an Ajax call, using POST, and returns an array created by a php sql query. Well... it's supposed to at least. I can get the ajax to return a very simple php echo. When I add the rest of the code necessary to build my db connect, even without trying to pass the array, I start to get an Exception Object, 503 error.

JAVASCRIPT

function updateYears(pageLoaded) {
  var yearSelect = document.getElementById("vehicle_year");
  var makeSelect = document.getElementById("vehicle_make");
  var modelSelect = document.getElementById("vehicle_model");

  $('#vehicle_year').html('');

  var $data = [];

  $.ajax({ url: '/new.php',
      data: {action: 'test'},
      type: 'post',
      success:function(result)//we got the response
      {
        alert(result);
      },
      error:function(exception){alert('Exception:'+exception);}
  });

  return false;

}

PHP

define('IN_PHPBB', true);
$phpbb_root_path = (defined('PHPBB_ROOT_PATH')) ? PHPBB_ROOT_PATH : './';
$phpEx = substr(strrchr(__FILE__, '.'), 1);
include($phpbb_root_path . 'common.' . $phpEx);

$db = new $sql_db();

$db->sql_connect($dbhost, $dbuser, $dbpasswd, $dbname, $dbport);

// We do not need this any longer, unset for safety purposes
unset($dbpasswd);

if(isset($_POST['action']) && !empty($_POST['action'])) {
    $action = $_POST['action'];

    switch($action) {
        case 'get_vehicle_makes' :
            get_vehicle_makes();
            break;
        case 'get_vehicle_models' :
            get_vehicle_models();
            break;
        case 'test' :
            get_vehicle_years();
            break;
    }
}
//Populate a unique list of vehicle years - this only runs on page load
//The vehicle years list will always be the same regardless of make or model  - block_var = "vehicle_years"
function get_vehicle_years()
{
    echo ("good job");
    exit;
}

Now, there's a lot going on in the PHP file, but I am really just trying to echo ("test"); for right now. If I remove the code in the PHP file that is between, define('IN_PHPBB', true); and unset($dbpasswd);, it works, so I know there is something wrong with the db connection code. The include statements are fine, because I don't get an error saying the file doesn't exist. The connection credential variables are also fine, because I get those from the config.php file that's included. I'm at a loss, and could really use some help.

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