解析错误:语法错误，C:Program Files (x86）EasyPHP-5.3.9wwwInven

我是PHP新手，收到消息解析错误：语法错误，第25行..中的意外T_VARIABLE。如果有人能帮助我解决这个错误，我将不胜感激，因为它真的开始给我带来压力。一直在织梦者上，它说错误，它说$Username=...但我似乎无法修复它

<?php
    $host="******"; // Host name 
    $username="******"; // Mysql username 
    $password="******"; // Mysql password 
    $db_name="******"; // Database name 
    $tbl_name="avaya"; // Table name
    mysql_connect("$host", "$username", "$password")or die("cannot connect"); 
    mysql_select_db("$db_name")or die("cannot select DB");

    $con = mysql_connect("localhost","root","");
    if (!$con)
      {
      die('Could not connect: ' . mysql_error());
      }
    mysql_select_db("inventory", $con);

    $addavaya="INSERT INTO avaya_pabx(critical_spare_id, serial_no, ,comcode, version, circuit_pack, classification, location, availability, date, client)
    VALUES ('". $_POST['critical_spare_id'] . "', '" . $_POST['serial_no']. "', '". $_POST['comcode'] . "','". $_POST['version'] . "','". $_POST['circuitp_pack'] . "','". $_POST['classification'] . "','". $_POST['location'] . "', '". $_POST['availability'] . "', '". $_POST['date'] . "', '". $_POST['client'] . "')";
    mysql_query($addavaya,$con)
    if (!mysql_query($addavaya,$con))
      {
      die('Error: ' . mysql_error());
      }
    echo "1 record added";
    mysql_close($con);
    ?>