ทำไมไม่ยอม INSERT INTO เข้าตาราง?? เข้าได้เฉพาะบางตัว

<?
session_start();
?>
<?php
$Session_name = "default";
$host = "localhost"; // Server
$username = "root"; // User Mysql
$password = "1234"; // Password Mysql
$database = "computer"; // ชื่อฐานข้อมูล
$table = "useronline"; // ชื่อ Table



if ($Session_name == "default") {
session_start();
}
else {
session_name("$Session_name");
session_start("$Session_name");
}
$SID = session_id();
$time = time();
$dag = date("z");
$nu = time()-600; // Keep for 15 mins
$mb_Status = $_SESSION["mb_Status"];
$mb_id = $_SESSION["mb_id"];


mysql_connect ($host, $username, $password) OR DIE ("Could not connect to MySQL");
mysql_select_db($database) OR DIE ("Can't select database.");

$sidcheck = mysql_query("SELECT count(*) FROM $table WHERE SID='$SID'");
$sid_check = mysql_result($sidcheck,0);
if ($sid_check == "0"){

mysql_query("INSERT INTO $table (SID,time,day,mb_id,mb_Status) VALUES ('$SID','$time','$dag','$mb_id','$mb_Status')");
} else {

mysql_query("UPDATE $table SET time='$time',mb_id='$mb_id',mb_Status='$mb_Status' WHERE SID='$SID'");
}




$count_users = mysql_query("SELECT count(*) FROM $table WHERE time>$nu AND day=$dag");
$users_online = mysql_result($count_users,0);
echo "<div align='center'><img src='icon/user_online.gif' width='20' height='20'/>&nbspจำนวนผู้ออนไลน์ $users_online คน<br><br></div>"; // echo จำนวนผู้ online ออกมาก

mysql_query("DELETE FROM $table WHERE time<$nu");
mysql_query("DELETE FROM $table WHERE day != $dag");

mysql_close();
?>
<table width="100%" border="0">
<?php
include('config4.php');
$sql = "SELECT * FROM useronline,tb_member WHERE mb_id=mb_id and mb_Status=mb_Status";
$result = mysql_query($sql);
while($data = mysql_fetch_array($result)){
?>
<tr><td>
<?php
if($data[mb_Status]=="member"){
echo "<font size=1px><img src='icon/check-user-icon.jpeg' width='20' height='20'/>&nbsp&nbsp;<font color='#000000'>$data[mb_user] ('สมาชิกทั่วไป')</font></font>";
}else if($data[mb_Status]=="bit51"){
echo "<font size=1px><img src='icon/check-user-icon.jpeg' width='20' height='20'/>&nbsp&nbsp;<font color='#0000FF'>$data[mb_user] (สมาชิก 'BIT51')</font></font>";
}else if($data[mb_Status]=="admin"){
echo "<font size=1px><img src='icon/check-user-icon.jpeg' width='20' height='20'/>&nbsp&nbsp;<font color='#FF0000'>$data[mb_user] ('ผู้ดูแลระบบ')</font></font>";
}
?>
</td></tr>
<? } ?>
</table>